[L]et's not forget at the moment that 'HTML5' is still in development (it's still not finalized), yet it's used in production now which ofcourse is actually a fubar thing to do..
Well, maybe, but not as fubar as trying to be compliant with all the various HTML "standards", including XHTML and MSHTML and iHTML and XML and ... ;-)
Anyway, I'd expect that HTML5 is following google's lead, and will be in Beta until all of us have shuffled off this mortal plane. It worked for google; it'll probably work for HTML5.
And so far, I've found that switching to HTML5 produces better compatibility than any other HTML version that various organizations and corporations have declared "standard". There are the usual insanities of trying to make pages work on MS browsers, of course, but if you're reasonable about dragging your feet WRT the newer HTML5 features, you tend to find that your pages work reasonably well with all the common browsers except IE6. (Well, OK -- and except for Safari on the iPhone. ;-)
Basically, the HTML5 gang has done a fairly good job of figuring out ways to thumb our noses at the corporate powers who are constantly trying to throw monkey wrenches into the Web's inner workings. Going with the HTML5 approach, and encouraging them to keep up the good work, is a feasible strategy to make things work about as well as we can expect in an environment of government and corporate sabotage attempts.