Okay, this was a weird one. When I setup the new logging so that awstats would work, it meant an extra file handle open in each user's name so that it can log stuff. This apparently exceeded some limit, and it didn't allow a new ssh process to be started then. If I stopped apache, then the logins worked fine. The limits in question were set to 70 processes each user, and as far as I can tell, no one had more than a dozen. I removed the limits and ssh works normally again though. I'm sure I must've put those there for a reason however, so no one do anything stupid like forkbomb the server, okay? :-P