Yeah, the most I've seen on chat is like 4 ppl. On some site, like the UK mantis forum, you are automatically logged into chat once you access the site. Personally, I like the topics better because you can always go back and people can join/post at any time and the information is saved. Sometimes valuable information is lost in chat, since there is no log.
I do like the idea of hosting monthly chat sessions where people just hangout. Which reminds me of Google hangouts, where we can video chat. Perhaps start one for mantidforum?