i like much of what's already been said. I do think, an idle option, as Castaway mentioned - would be a good thing, since it's often hard to determine who's there and who isn't.

i'd queue it to say 15min's w/out having made a comment or manually clicking the refresh button or link, if possible.

but IDLE, mind you - not kicking'em out of the chatroom. The reason being, that oftentimes, people - myself included - would like to participate in the conversations, but because of the topic of the moment, may not be able to contribute. (so, i'll watch the conversations, until someone says something, which i can add to.)

i also like the opt-out feature mentioned by Zero_Flop. Not everyone wants to or has time to chat. Sometimes, one just wants to pop, grab something, and leave. (Is the Other Users category needed? I do like it, but i'm not sure, what i would use this function for - outside of maybe sending them a private, timely message.)