I disagree. I do not think debating whether or not Twitter should or shouldn't be used as a chat app is necessary. It offers the functionality, therefore it WILL be used as such. Might as well enjoy it along the way. If you use Twitter through the web to update (i.e. NOT as a chat platform) it is okay to include it wherever you want. If you use it like a chat app (like me) then simply be savvy enough not to pollute everything with senseless tweets (again, like me! dammit, my ego has a leak… brb)

Skype, Google Talk, MSN, etc. is not a solution at all since it is pretty much peer-to-peer and you'll never know who is hosting what group chat where.

IRC could work, but it is not web integrated. Ugh, there is no easy answer it seems!