Back in the day I was a huge MUD player, but that went by the wayside quite a while ago. I do not know about roleyplaying though: I thought serious roleplayers tended to play MUSHes, not MUDs, per se, though in popular parlance the former is basically a category of the latter. And then again, the sort of people who still play MUDs are probably a somewhat different sort. Last MUD I really played much was God Wars II: The Supernaturalis. And it has a pretty in depth combat system that requires a lot of attention, reflex, and typing.