Personally, I'm very excited by Wave. I think it's going to be great (as in Google usually make quality stuff when they put their minds to it, I think it will be free enough to use with good conscience, and it will be uber-powerful)
I'm also willing to bet on the ultra-conservatism of the majority of users, and predict that they WON'T GET IT. This will have made hardly a dent on either email or M$ Office use by this time next year. Most people will be confused (rather than delighted) by the blurring of email, document editing and real time conversation. Early adopters won't be able to use it to send emails or share documents with late-adopters, so hardly anyone will be able to use it in enterprises etc.
The people who'll be most affected by this are 37 Signals, Huddle, SocialText etc. who are trying to sell web-based project management or enterprise blogs and wikis to early adopters. It's gonna be a tsunami in that market.
Nevertheless, can't wait to play with it.
Couple of interesting posts