IE9 officially released yesterday:
http://www.beautyoftheweb.com/
I've been using the release candidate extensively to future proof all my sites and I've been trying really hard to reserve judgement. As much good as MS has done in IE9, there were a lot of omissions (at least in CSS3) that were going to make it continue to lag behind Mozilla/Webkit/Opera browsers. Like text shadow. Probably a top 5 most-used CSS3 property.
Sadly the official release didn't add support for it. And the DOM inspector doesn't update after initial load, which means it might have been useful a decade ago but useless today. Box shadow implementation is noticeably different from mozilla/webkit (blur parameter isn't working properly). Some great typographic pseudo classes are ignored, no border images, no css3 keyframe animations(!!!!), no flexible box model.
For the average user, none of this really matters, because guys like me will continue to make websites that look right in IE9. Most sites won't look quite as cool, but most IE users will remain blissfully ignorant because it's their primary browser. Javascript/HA performance is awesome, it finally has a reliable rendering engine for CSS2 stuff, etc. All that stuff is great, but somehow I feel like I've been checking out a girl from behind, with a super sweet ass, but she just turned around and looks like Courtney Love.