I'll be honest, I only ever used Wave for about 30 minutes, but the potential for a new vendor agnostic collaboration platform was pretty exciting. I can't see it picking up pace now that it's an Apache project. Sad. I think we're stuck with email for the foreseeable future for vendor-agnostic long form communication.
Since the article didn't mention it, there's http://rizzoma.com/ which hosts a rather nice version of Wave.