My first impression, I really enjoyed exploring the Google Wave. I like that it's live chat, read as your partner type. It already has many extensions like: Video Chat Experience, Conference, Sudoku, Map Gadget.
In the wave, anyone can add multiple participants. Participants can reply any time and anywhere within a wave, and they can edit content and add more participants as a wave develops. It's also possible to rewind waves with the playback functionality, to see what happened, and when.
Here is the video that you can find on http://wave.google.com/help/wave/about.html
If you want to try it I can send some invites out. In the comment box do not add email, but rather type it in the field for email. Those who come first are the first to be served.