Microsoft has opted for a conservative approach to new web technologies in IE9. While the nearly complete Firefox 4 and the recently released Chrome 10 support more of the HTML5, CSS 3 and web API stack, IE9 is a huge step forward for Microsoft. IE9 offers support for the most widely used elements of HTML5 — like the new audio, video, canvas and semantic tags. Still, Microsoft has decided to pass on many of the new APIs. Cutting edge web tools like the offline web applications API, the File API, Web Workers API and the Web Notifications API won’t work in IE9. That’s bad news for web developers, but it’s also bad news for IE users since the web shows no signs of slowing down to accommodate IE.
If you want the full list of IE9 features, go to the IE9 Guide for Developers. Designing websites for Internet Explorer (all of them, even v9), is like paying alimony: the marriage was a bad idea to begin with, and we’ll be paying for it for years to come.
A few posts ago, I defined a layout that degrades gracefully is one that works on Internet Explorer, now I classify Internet Explorer 9 as legacy software.