Interesting in light of Apple's push :
http://www.infoworld.com/d/developer-world/w3c-hold-html5-in-websites-041
http://www.infoworld.com/d/developer-world/w3c-hold-html5-in-websites-041
Spot on.
I don't know why so many people seem to think HTML 5 will magically eliminate browser inconsistencies.
It will definitely help with those inconsistencies especially with IE9 supporting it.
The point of the W3C (they are the ones writing the standard in the first place) is that the current draft is not complete and the problem with implementing now based on browser implementations is that in the future, you might introduce standard inconsistencies, where you're using parts of the draft that never made it to the standard or parts that were modified but that browsers implemented early and of course, wrongly.
Also, right now, a lot of HTML5 CSS properties are still browser dependant, using the moz- and webkit- prefixes. When browsers drop the prefixes, you will have to update your CSS.
Basically, the W3C is advising against using the draft in its current state. They should know what they are talking about.
While the W3C knows what they are talking about, I think the best approach is the one described above. No sense in not trying it out in a beta form, like what YouTube is doing.
If you are aware of the W3C warning, you won't be surprised when things stop working.