Iii don't know? I've never had to boot anyone. But I know that there's no obvious "get me out of this chat" button. If I remember right, you have to right click something or find something that says "leave this chat" because clicking the little X in the corner doesn't actually do it. I've had chats in my list for over a week because I keep forgetting to leave them, but you CAN remove them. It's just kind of inconvenient.
Also! I used to have a Mac (RIP my Macbook) and have used both Adium and the desktop version of GChat. Only the actual gchat client supports group chats, though. I was also recently using our Mac desktop while my PC was in the shop, and the current version of AIM works just as well on a Mac as it does on the PC. Only downside is that despite being able to use Gchat from the AIM client, you still can't be in a group Gchat from it, but most people I talk to use AIM anyway.