HTML 5 is two things: a codification of how browsers parse documents and handle errors, and a slew of new features for HTML and JavaScript.
The first part is more of a set of guarantees that browser vendors can agree upon, and I believe it's largely based on IE's behavior.
The new features are already slowly trickling into browsers. For example, Firefox, Opera, and Safari all implement <canvas>. There are a number of other features that are already implemented in browsers, which you can read about here: http://wiki.whatwg.org/wiki/Implementations_in_Web_browsers.
So, right now some new features are closer to the mainstream than others, especially where there are 3rd party implementations for IE (like ExplorerCanvas, and Google Gears which will probably have HTML5 APIs at some point). I wouldn't hesitate to play around with these new technologies, especially at the rate they're being implemented.
The first part is more of a set of guarantees that browser vendors can agree upon, and I believe it's largely based on IE's behavior.
The new features are already slowly trickling into browsers. For example, Firefox, Opera, and Safari all implement <canvas>. There are a number of other features that are already implemented in browsers, which you can read about here: http://wiki.whatwg.org/wiki/Implementations_in_Web_browsers.
So, right now some new features are closer to the mainstream than others, especially where there are 3rd party implementations for IE (like ExplorerCanvas, and Google Gears which will probably have HTML5 APIs at some point). I wouldn't hesitate to play around with these new technologies, especially at the rate they're being implemented.