Google chrome html5 support
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To answer your question: It's only fully supported in Opera and Chrome. Full support by all browsers isn't to be expected in the near future.
Well, I don't know about any official references, but I can at least talk of my experience:
At the moment my google chrome 8.0 scores 231 of 300 points in the http://html5test.com/.
Parsing Rules, Canvas, Audio, Geolocation, Communication (Sockets and the like), Files and Workers have 100% points, so they are fully implemented.
Video, Elements, Forms, User Interaction, Application Cache and Storage are mostly supported. But your example, the datepicker, is not supported. It is just rendered as an input field with two arrows (up and down), with which you can cycle your date up or down.
Local Devices (device element), Microdata and WebGL are not yet supported.
But the Chromium 10.0 I have at home supports WebGL.
There isn't an official one I don't believe but this is by far the best I've ever seen: