A lot of the analysis of Wave so far has (stupidly) focused on the web app that Google was showing off, on the whiz-bang HTML5 bullshit that ultimately doesn't much matter. I think it's really important to think of Wave not in terms of the front-end they were showing off, but rather in terms of the underlying protocol that powered it. Google envisions it as a sort of SMTP 2.0, powering most person-to-person communication on the internet; if (and only if) the industry gets behind it unilaterally, I think it has a real chance of success.

The paucity of existing documentation can be forgiven, but only to a point -- it's definitely on Google to make the complex elements of that protocol (and there are many) developer-accessible. As cool as the technology is, it'll wither and die without proper support.