I got into Fresh and Saltwater Aquariums for some time but it was "not for me"... never had much success there. I have toyed with the idea of dusting off my old equipment for another go at it.
Oddly enough, I have about 2K gallons of koi/goldfish ponds (3 in total) spread out on my property that have been very successful and bring happiness to the neighborhood, myself, and the neighbor's cat. 
When time from regular work was available I spent my free time restoring several old cars, tractors,etc. Eventually arthritic hands and a diminishing bank account put an end to that hobby.
HO trains had been a sometime hobby but at the beginning of the 1980s and frustration with the rivet counting culture of HO, I gave the equipment to one of my sons. Then I fired up my 2333 Lionel Southern AA diesel shelf queens and went with transition era O-gauge for the last 34 years.
However, since 2008 due to age and health issues, and a relocation, I have dismantled two large layouts. Currently I am in process of selling all my trains except for a half dozen of my engines for use with short consists on a small attic layout.
I have enjoyed all my hobbies but none as much as O-gauge trains and Southern Railway history.
[old photos illustrate some suvivors of a really expensive hobby, '69 Caddy, '55 T Bird and our old '49 Dodge farm truck].
Photography, stamp collecting, model airplanes, and genealogy.
Art
Gave up: Chasing wild women and raising heck. Accidentally met a nice girl, fell in love, got married, gave 'em up.
Still do: The trains, obviously; build, fly, crash, repair model planes; make music; fitness cycling; photography; reading (no "literature" anymore, mostly mystery/detective novels).
Pete
When I was still working I used to say that the job got in the way of my hobbies. I have to say that I have pursued and continue to pursue multiple hobbies chief of which is toy trains. Other hobbies include swimming, cycling, hunting, fishing, hiking, writing and American Civil War history. So far I have not dumped any of them and I am going to try to hang on to all of them as long as I can.
I was restoring old cars, would flip a car every 2 to three years. It just got to expensive, insurance, parts, labor and time.
At the time I was engineering cars, and to come home and work on them just gave me a headache.
Next was boating, that did not go far. Anyone want to buy a boat?
Should have kept the last muscle car I restored.
Was going to do some R/C monster trucks or WW2 tanks... never started.
Golf. The Mrs. has been playing since she was 7, still make her play from the Men's tees... I keep that one going
Fishing. Well lets just say every time pick up a fishing rod it cost me my wallet, so killed that one.
Seems I have had quite a few in my almost 64 years. I collected baseball cards (still have most and that includes a lot of Mantles and Aarons), pennies, stamps (only with fish or butterflies on them), and fossils (especially of the Ordovician Era). I have maintained aquaria and terrariums (still do, have a small collection of poison dart frogs and turtles...I am an Ohio Certified Volunteer Naturalist and have state permits), bird watch, kayak, and of course, baseball. Heck, at 63 and thinking I had retired for good, I agreed to be the head varsity baseball coach this season. My trains have had to take a back seat this spring.
Rick
1) Started in HO and ditched that for O gauge
(O gauge or NO gauge)
2) Plastic model kits, kits started to become to expensive.
my 1rst 1/24 scale model cars were bought at the local
drug store for $5. they now run from $15-$25 each.
3) HO scale slot cars. My grandmother warned us that if we didn't
pick up our toys she was throwing them away. Came home from
school one day and she had picked up our slot cars and thrown them
away.............thanks a lot grandma1 
Old hobbies never die, they just fade away...
Rusty
started in trains, went to coin collecting, still was in to trains, then computers hit. put everting else aside and spent over 10 years in computers spent so much time collecting older computers making them run if they did not. when i was in my early 20's hurt my back. could not do computers like i use to could not lift them or carry them. so in one swoop i called some one i know and asked him if he wanted all of it. i kept a few laptops but that was it. gave him about 4 truck loads of computer equipment. after that i said god give me a sign of what hobby i should be in. no sooner then i said that then my grandmother said why not look online for trains. and i said if i find a rock island northern for a good deal i will go back to trains as a hobby. i found one that after repairs and shipping cost me under $140. since then i have been hooked on trains once more.
I've been into O gauge for as long as I can remember, it first started with pulling out my uncle's old # 1107 Texas Special freight set out of my grandmother's attic once in a while when I would stay with her during the summer months. The set still exists and I kept it at my house for a decade after she passed away, but my uncle wanted it back a couple of years ago, which I was more than happy to do (it was his, after all). Eventually my grandmother she bought me my own set (the first Black River freight set MPC came out with). That set is long gone after I went into more scale sized stuff back in the early/mid- 80s (Weaver, Lionel Std. O, etc.). Even had a tabletop layout set up in an empty bedroom before I left home.
Like a couple of others stated here, I also got into scuba & sky diving (still do scuba whenever I can), and I also used to build computers & set my own LANs up, even using the fully robust but now quaint Novell Netware servers (I'm also in the IT field). I also enjoyed travelling, visiting state parks, going up & down the CA coast line, explore old ghost towns, etc.
But even when other interests took up my time, I never fully got out of trains; I'd still set up a temporary loop on the floor whenever the mood struck me. I now have an 8 X 16 layout downstairs. I run primarily scale 3 rail trains, but I still have a somewhat sizeable collection of MPC (mostly from the Famous Name RR series) and some of the billboard quad hoppers and I also have some postwar and I'm still having fun.
I scratch build models of ships and planes, Building structures. I also like competition shooting. All of the other fun stuff is on hold as we build out the basement, sheet rock, wiring, framing, drop ceiling, and build the biggest crapy basement layout in VA.
I have a waterfront seen in mind and it will have some ship in it. Airplanes overhead and some modified or scratch built structures here and there.
Hot rods, built a 32 model B roadster with 65 Mustang running gear (a mishap left only the running gear). Next, built a 31 model A roadster, complete with 348 Chevy with two fours. Restored a 66 Mustang in the early 90's, then ended cars. Collecting 50's art glass and Murano Glass clowns. After spending lots and lots of money, the bottom fell out of the collecting market, now I'm stuck with vast collections and nowhere to sell them. Oh yeah, that reminds me, I got into stocks when the market was at a peak, and then it took the BIG dive, and now my stocks are worth less than 50% of my investment.
THIS IS A HEADS-UP. IF YOU SEE ME SELLING SOMETHING ON THE FORUM, BUY IT, BECAUSE IT'S FOR SALE AT WAY LESS THAN I PAID. I SELL EVERYTHING AT A LOSS, BUT MAKE UP FOR IT IN THE VOLUME.
speaking of hobbies: anybody ever chck out this site for plastic model kits.
there are also some train kits in brass.
1) Mostly O gauge since I received my first Scout set in 1958...I still have it; although a bit ragged after many years of use.
2) Dabbled in HO for a time; found it entirely too small to work on - dumped it 25 years ago
3) Motorcycle restoration and Motorcycle riding - still going strong
4) Flying - both my wife and are are pilots, and have a plane out at the local GA field
5) Model building (mostly aircraft), sample of a second prize win at Nanton Bomber Command show in 2013 (link to F-104 at 6:58 mark)
http://www.youtube.com/watch?feature=player_detailpage&v=zLQ44zW-wXQ#t=421
r0d
It seems my hobbies have always evolved. I am a collector my whole life and just change what I collect it seems. I started with baseball cards, Stamps, Coins, Beer cans,Slot cars and then into trains as I got older.. I have always loved cars and enjoy drag racing and have 3 cars I enjoy. I used to quit hobbies before and then later wanted them back.lol What I have learned is I just put it aside for a little and I seem to come back. Better than selling it all and starting over.. But it seems the chase and learning something new motivates me.. I tell people its a Ism... Like alcoholism, I cant help myself..But its fun and I have met some great people on the way.. I now only have the cars and enjoy trains and slot cars still. But the quest to have one of everything seems to be fading..
Cars:
2011 Ford Raptor 412HP
2013 Taurus SHO 365HP
2013 Shelby GT500 662HP
2014 Focus Electric
1970 VW Beetle 53HP
One of the things I've noticed, that some Hobbies, when it comes times to sell out, aren't that easy to find buyers, yet dealers are all over you to sell at a nickel on a dollar value. Finding this out on autographs, pocketwatches, wall clocks, some military items, and some firearms. When I was in the Mid-West, there were all kind of shows to buy, sell or trade. Not so true here in Florida.(same for buying train stuff. Here in Florida its mostly mail order or driving several hours to a Hobby Shop), But have all kinds of Dealers willing to buy it off me.
I am mainly into O gauge trains.
Got involved some with high performance cars for a couple of years but gave it up before getting married.
I have some old Aurora H.O. slot cars from 1965 to about 1977, and a couple of newer cars too. Only raced the cars with my friends; either at their house or my house. I had a nice four lane track layout about 4 feet by seven feet before going into the US Army for six years.
My next layout will have a place for my H.O. race cars. Have a couple of H.O. trains but don't like them as well as the O gauge trains.
Lee Fritz
Drag racing. My last was a 1969 Camaro Super Gas (9.90) car. As far as money is concerned, model trains is chump change compared to drag cars.
One of my co-workers who still races totally destroyed a $25K engine on it's second pass. You can take a $50K car and reduce it to scrap in less than a minute (including the burnout). The best part is you might "win" your entry fee back and maybe a nice plastic trophy. Time was I'd win marching through the rounds turning 9.91 or 9.92. Today I'd be on the trailer after the first round if I was lucky enough to qualify.
I've been "in" and "out" of Golf through the years. Currently I'm "in".
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