I’ve been testing out Google Wave for project and writing collaboration. So far it seems to work very well for those types of things. But at the same time it can be used like this hypermix between email and twitter; which I imagine if you participate in too many waves would get overwhelming very quickly. That said, it’s very awesome in lots of ways, and while still in preview there are lots of things to be ironed out. For example, I think there needs to be incredibly granular controls on posts/blips. Technically any blip posted to a public wave can be edited by anyone. I think this is fine in general for conversations, but doesn’t work so well for the message the introduces the wave or provides rules for the wave.
Even with the 100,000 plus add in, I still feel like the audience needs to be larger, before we get some real tests for certain types of things. Like being able to invite a group of people to a private wave, and collaborate. Since the likelihood of your collaborators also having a Wave account is thin; you can either make a wave public and try to collect whoever is interested or keep it private with 1 or 2 people.