I once had to take a train from Rome to Amsterdam at the last minute because Ryan air cancelled my flight. Hours of standing near the bathrooms until a very kind Italian lady with some kind of skin condition (her face was covered in warts) invited my friend and I to sit for the last hour of the ride. She also gave us a little pastry.
Anyway, depending on the country of origin, European trains on a severe budget (unless they have improved significantly in the past 10 years) are just as uncomfortable (if not more so) as flying cheap in my experience.
My preference is as follows:
Dutch trains are fucking fantastic.
German are ok, but the trashcans were usually full.
French trains were like German trains, but slower and less punctual.
Italian and Spanish trains were the worst. Once on an overnight from Paris to San Sebastian I was in a sleeper car and the train hit a bump in the track just over the border, causing the ladder to fall and hit a lady's arm that was dangling off of the bunk. Nothing like a train car full of strangers, stifling laughter in the middle of the night.
I really do love traveling by train and it's a shame that most people don't want to take the time to use them, but then, people seem not to wander around. In the US, Amtrak did a writing fellowship wherein people could submit proposals for writing projects that involved train travel and if approved, the writers would be able to travel to their desired destination and back. Good idea, but it's not enough. I have the feeling that in the US anyway, more people would wander if it were cheap, given that more and more it's becoming clear that going to college might not be The Thing for people to do right out of high school.