I just got my Wave account a few days ago, and it's awesome. However I didn't get the Invitation wave, so I can't invite any of my friends, so it's kinda boring just now. I actually don't have the Settings either, or the welcome message, so I think my account fucked up a little bit.
Still, I can see it being an excellent tool for collaborative programming. There's an awesome little app for syntax highlighting, add kasyntaxy@appspot.com to your wave, and post a new blip with #!python at the top (replace Python with any other language - most work), and type your code. There's a lot of other cool apps in development too, I think Wave is gonna be awesome when it's released publicly.