I've used trains when I could to travel for business. A few observations. Until they have the same infrastructure (car rentals, public transport, etc) that airports have at their destinations, it is a non-starter. Arrival times at cities along the route can be inconvenient. Pulling into a city at 2AM or 1PM is generally not convenient. Being delayed an hour or more, regularly, is not exactly an endearing feature. I used the same formula for any trip - if driving takes 125% or less time compared to any other method, drive.
Brendan