In fact, after using Wave for these projects, email suddenly seems a little too disjointed. That said, email is more universal, a proven technology for the most part and pretty much baked into our daily lives. Wave is still a Google Labs product and perhaps more prone to failing so relying on it too heavily is risky. Fortunately there are ways to backup waves by exporting them and when Wave becomes an HTML 5-based service, hopefully some sort of offline capability too.
I just watched a video about Novell Pulse, Novell’s Wave implementation, which nicely illustrates some of what Wave can do as a federated platform: