Microsoft revealed some first details of Internet Explorer 9 at the Microsoft Professional Developer's Conference, as reported by Mashable today. Only in development for three weeks, there's still quite a lot of time before it gets to market. According to Mashable, Microsoft did have the following to say:

While I can understand Microsoft's position that HTML5 is not set and therefore may not support everything in the barely-draft spec, some of the elements seem pretty well locked in with only minor syntax and rendering issues left to suss out. To that point, I hope Microsoft can at least work in that support. The CSS support is a whole different story. Given how long the CSS2 spec has been out there (since 1996), it would be nice if they'd commit to fully supporting it, even if they aren't yet sure about CSS3 support.

As Internet Explorer's market share is slowly eroded by Firefox, Safari and Chrome (on a trend that, if projected as a simple linear graph, would see IE go away by 2021), Microsoft is motivated to increase the overall performance of its next browser. Unfortunately, given the slow pace at which IE version 8 is being adopted over older versions (still at 34.1% of all IE installations after release March 19, 2009, versus IE7 at 37.6% after release October 2006 and IE6 at 28.3% from way back in August 2001), it is quite likely that even after IE9 is released it may be years before developers can rely on its features on public-facing web sites.