W3C, the World Wide Web Consortium has deemed HTML5 not yet be ready to deploy in web applications. Microsoft, Google, Apple, Mozilla, and Opera have all added some bit of support of the HTML5 specification into their browsers, but W3C claims that it isn't polished enough, nor supported enough for general use yet.
Philippe Le Hegaret, from W3C said that most of the current implementation is in the beta versions of browsers and that the APIs, as well as cross-browser compatibility just aren't up to where they need to be to implement the features into websites. Infoworld reports that Le Hegaret still acknowledged HTML5 as a "game changer," just that as of now using Adobe's Flash or Microsoft's Silverlight is a better choice until the features can be properly documented and supported.
Apple has been pushing HTML5 with leaving off support for Flash on their iOS devices, but the W3C does not feel that it is time to retire Flash yet. Currently they are aiming for HTML5 to be feature complete by mid-2011, and expected to be approved in two to three years. Le Hegaret still sees huge gaps in the new HTML specification, such as lack of a video codec, Digital Rights Management support, and authoring tools.
The lack of an agreed video codec lies in patent issues since HTML5 is to be an open platform. H.264 however was recently stated to stay royalty-free. The codec which is already in use by Interent Explorer 9, Chrome, and Safari has a good chance at becoming the standard, knowing now it will stay royalty free. DRM in an open system wouldn't work out, as "it would be broken by a hacker within two days," Le Hegaret stated. Authoring tools are also at a loss, but Adobe offers one that works in conjunction with their Creative Suite package.
W3C may see HTML5 as unfit to use as of now, but there still are plenty of components that are well supported across browsing platforms. Webmasters just need to be cautious on what they choose to include as of now for maximum compatibility.
As I have said earlier: It is ok that people jump off the train when they believe it is the right time, but it is safest and best to wait until the train reaches the station.