To further illustrate my ignorance about this chat client, I'll have to ask what exactly is a Chat PM? Is it different from a regular PM?

And what's the difference between the number of chatters listed at the top of the page & the number shown on the chat bar at the bottom? (If someone has been trying to chat with me via that bottom one, I apologize - never really knew what it represented. I only just realized that clicking on it showed the username of the chatter shown & didn't dump you straight into an ongoing chat...).

Since the subject of potentially controversial/triggering chats has come up, can any of the 'rooms' be restricted to certain invitees? That way, such topics could be discussed between interested parties only.

Yeah, I'm more of an email dinosaur.