I tried, oh how I tried to do something with this tool.
One of the thing all good software needs is the ability to give you something if no one else is out there. Well maybe not email, but in Second Life you can go to an empty SIM and still explore, and SharePoint is useful even beyond collaboration.
But with Wave it like you have a chat group with no one on it. I can't really see how it is more than a rich chat group, but you have to go find the members and talk them in to paticipating.