I got an invite to Google Wave a couple of days ago, and I've been poking around in it ever since, finding good public waves to follow and trying to figure out how I can best use it. So far it seems to function best as a forum/chat hybrid. It's still really buggy and has scaling problems for sure, but I think it could be very useful as a project management tool.
Are you on Google Wave? If so, how are you using it?