I'm waiting for the O'Reilly book on it! Seriously, it is in beta everywhere, so I wouldn't run a business with it. I have certainly read and understood the current standard, and I'm ready to start using it.
When XForms/WebForms is in its final form (what I referenced was the almost-final draft) I will feel more comfortable developing with it. The idea of specifying abstract UI, of course, is not new, but I really like the way that WebForms does it, because I can see that working in a Java Swing or Perl/Tk environment as well with some small modifications.