i have done 24 and even 36+ hours in a train multiple times (madras to calcutta, madras to new delhi, madras to bombay, etc) and arrived quite fresh and rested (of course not comparable to sleeping on my own bed). of course india is a third world country, so how can it compare to the leader of the free world ;-).
i travelled venice -> rome (8 hours?) in a train (in one of those couchettes are whatever they call them) and that was perfect! i am not sure another 8 hours in that train would have made me cranky (rumpled perhaps, but i am rumpled most of the time, anyway, being a geek).
i would pay the same amount of money, and gladly take a doubling in time, with current levels of comfort, to substitute any plane travel in the US with an amtrak trip. i know its been gone over a few times, but i really fail to understand why newark -> chicago should take more than 24 hours by train (at 2-3 times the cost of a flight), other than a lack of govt support. i mean, it can't be the geography or price of fuel, or some such: i did the same trip (reverse direction: chicago -> newark) on a frigging motorcycle, in under 24 hours, for dog's sake!
--ravi