But... Topics are meant to live! Forever and ever!
Well, maybe. ;p
Anyway, since my time here, and assuming that my memory is serving me right (and it'd be a surprise if I had much of any processing power left), I'd say we've had (at least) four permanent bans, not including any self-imposed banning that may have occurred once (memory's foggy on that one).
One of them, if I remember correctly, was a Neo Nazi or something. It was the earliest ban that I know of, so it's no surprise that the details have slipped my mind. I just remember Coruscate having fun with them before they were banned. Another got banned for the way they commented on things, and generally acted rude, without learning for each time they were called on it. Another was due to their actions in IRC, which could have lead to something illegal. The other that I can recall is the most recent, for continually doing what trolls do best as well as saying things that angered other users. The last one we had banned once for a week, and then we (sort of planned on) banned them for a few months. But, when the time came around to lift the band, no one felt like it, so...
EDIT: I hope what I mentioned was alright, Xia. I'm not the sort of person who's politically, socially or morally correct.