I have used coffee grounds that were baked well in the oven to give a dark rich soil appearance. No problem. It gives a different appearance that real dirt. I used real dirt also that was naturally finely sifted off of a softball field that gave a different but great appearance. I think that coffee grounds can have a place on the layout, but it should be kept dry. Probably the different results that folks have had is due to the different conditions where their layouts reside.
Rick
