I might have missed it in the video, but it wasn't exactly clear whether a wave server would be open source. So I looked and found this statement:

"This is just the beginning. To help potential wave providers get started, our plan is to release an open source, production-quality, reference implementation of the Google Wave client and server, as well as provide an open federation endpoint by the time users start getting access."

Good to know. For a minute, I was worried that they'd see more act like Adobe and be selling a wave server for $5K.

Social networking sites will be great places to promote this technology. ....and I was thinking about integrating a web mail client into D7. This changes everything :)