Wave is not for:
- Large groups of people (such as conference audiences) - too noisy and cumbersome.
- Individuals - the communication element is strong, so unless you have a split personality, you're better off organizing your thoughts in a document rather than a wave.
- Small groups working on single documents such as a manuscript or planning document. Google Docs or Etherpad works perfectly well with this without the complications of Wave.
And one more thing. Even if Wave is what email would look like if it were invented today (it isn't, this is just a one liner the developers were forced to come up with at short notice for PR purposes - the Google PR department must be one of the scariest places in history), disruptive technologies augment rather than replace preceding ones. (Television did not replace radio, radio did not replace books, etc.) So while we wait to find out what Wave is good for, lets bear that in mind. Paul Buchheit suggests the future of Wave is to be integrated into the other Google offerings, producing a realtime environment for GMail and Google Documents. And he's been right before.