Trav - 8:31 pm on Oct 7, 2010 (gmt 0)
I've seen this posted here and there, and it's kinda of a red herring. There are parts of html 4 and css2.1 that aren't supported by the current browsers, and yet everyone has found a way to cope.
One guy at the W3C is saying this, not the entire consortium.
The fact is, parts of html5 are currently supported by every browser. The parts that aren't can easily be omitted, and of course there are a number of workarounds (such as Sharp's HTML shiv) for those parts with spotty support. The only reason I can think of for not learning it and using what's available now, is if you plan on retiring from web-authoring in the next couple of years.
It's an evolving thing, and I suspect that by the time the standards body actually puts this thing to bed, we'll already be talking about the next thing in this same way. My feeling is (to paraphrase Gandhi): be the change you want to see in the world.