About three hours on the train, station to station (more like 4 if you measure door-to-door). Anyway, I think it's a fairly good distance, because I'm not really tempted to go back just for the hell of it, but when there's been a reason to go back (reading week, family funeral, getting a fairly specialist item fixed being the three reasons so far other than xmas) then it's not a major pain.
PS my careers teacher used to have a formula for a happy university experience. I can't remember what most of it was, but one part was "two hours away from home, girls!" - basically for the reasons above