I'd like to go a bit deeper about all of these to bring things into better perspective for developers. There were some very nice interviews on Channel 9 with the IE team.
That brings us to the next point. To pass Acid3 Microsoft with need to support a number of things presently lacking in their browsers: HTML5, Canvas and SVG. Since Eliot Graff, a member of the IE team, is helping on editing the W3C draft for the Canvas element, I expect them to add support for this at some time. Right now IE9 only scores 32 out of 100 on the Acid3 test. All other major browsers score 100 or very close. The team didn't say they wanted to achieve a score of 100, so there was definitely some abiguity there. For that matter, Firefox 3.5 only scores 93. But then, the alpha of Firefox 3.7 scores 96.
CSS3 Finally Comes to IE
Now lets talk about CSS3. In the PDC demo they showed IE9 rendering CSS border radius. They rendered beautifully in the demo, with proper anti-aliasing for smoothing of edges, even with animation. At present the following browsers support CSS3 border radius: Webkit, Mozilla, Chrome (Opera doesn't support this yet). Webkit and Mozilla's rendering of the border radius is excellent, even with animation. However, Chrome's rendering is substandard, displaying pixelation. It looks like Chrome does do any anti-aliasing yet. So the initial implementation of border radius in IE9 is on par with Webkit and Mozilla.
From GDI to D2D
IE9 uses D2D for rending. This has a big effect on text clarity and text animation. The team also demoed animated rounded corners using D2D. Christian Fortini, an IE team member working on the graphics backend, also mentioned box shadow. Christian who talked in length about animation, at one point mentioned that developers wanted better animation and transitions in their Web apps. Since he mentioned transitions, is this an allusion to CSS transforms and transitions presently supported by Webkit and Mozilla? Cross your fingers. Since they're using D2D, it should be trivial for them to implement box shadow, text shadow, CSS background gradients or CSS transforms and transitions. One thing you can also expect to see is improved Image scaling. IE9 off-loads this to the GPU for smoother and faster rendering.
CSS Selectors Test
And finally, CSS3 selectors. The test team showed IE9 running the CSS3 selectors test. This tests 43 different CSS3 selectors in 578 tests. IE8 only passes 349 out of the 578 tests. IE9 passes 574 of the 579. This is really great news for CSS geeks.