In HTML5's favor, Apple's iPhone and iPad will not support Flash, but are expected to gain support for HTML5 features as the standard matures. Similarly, Google's Chrome browser leads the pack in HTML5 support, and devices based on the company's forthcoming Chrome OS are expected to follow suit. Large Web publishers, however, have traditionally been conservative about standards support; even given a large HTML5 installed base, it may be years before the Fortune 500 is willing to risk the upgrade.
How to try HTML5 today
Some voices among the Web development community also urge caution. Although Microsoft plans support for HTML5 in Internet Explorer 9, for example, the software giant questions the wisdom of claiming support at this early stage. "Saying you are standards-based but then saying you are the most HTML5-compliant browser does not make sense, because the standard is not [complete] yet," Microsoft's Steven Sinofsky remarked in a recent interview.
Indeed, no organization is more guarded in its estimates of HTML5 adoption than the W3C itself. The HTML5 working group does not expect the standard to reach Candidate Recommendation status -- the feature-complete phase of the W3C standards process -- before 2011. Even then, the process of ratifying the standard as a W3C Recommendation is expected to continue until somewhere around 2022. If you're doing the math, that's 21 years from XHTML 1.1 to HTML5.
By any count, HTML5 is likely to remain cutting-edge technology for the next five to 10 years. Early adopters who would like to see it in action today can do so, however, albeit in a limited way. A number of pilot projects and demonstration sites that showcase the various capabilities of the new standard are available online; the key is choosing the right browser. Support for HTML5 features in Firefox is spotty. Browsers based on the WebKit rendering engine, including Chrome and Safari, work best. Ironically, that means Internet Explorer is also an option -- but only with the Chrome Frame plug-in installed.
Web developers, likewise, are free to experiment. Whole sites can be built with code that conforms to the current draft of the HTML5 specification, although results with current browsers will be spotty. One of the best online resources for would-be HTML5 developers is Mark Pilgrim's excellent Dive into HTML5, which includes, among other things, a detailed guide to navigating the complex world of the HTML5
video element and the various codecs supported by current browsers.