If a "modern OS" is required for hardware acceleration, how comes Mozilla intend to add hardware acceleration to Firefox 4 on Windows XP starting with the next beta? There's something fishy here.
Moreover, from what I could see, a "pinned website" is a shortcut that retrieved the website's icon and loads IE 9 with a switch that makes it load with the favicon set right before the back/forward button.
As for site-dependent customizable toolbar colors, I don't give a month after forced install before there's an exploit out there that can subvert the browser.
And, "mostly positive reviews": please, how many of these merely say "IE 9 will be better than IE 8". Well, yes.
It'll still be behind other browsers in speed (on my machine, Firefox 4 beta 6 runs circles around it when it comes to UI responsiveness), required resources (ditto), standards compliance, stability (yes, I did crash it, several times, and it never recovered), availability (Vista/Win7 only), ease of use (I dislike Chrome due to its minimalist interface, although it is reactive and still rather complete; IE 9 manages to make a minimalist interface look CLUTTERED!), attractiveness (the new logo: take the old one, dip in bleach for a few days, leave to dry in the desert's sun for a few months; enjoy) and cleanliness (I reported a bug in a CSS3 feature they decided to implement, in Preview 3, or 3 months ago; it's been acknowledged, but is still not fixed).
The best IE ever. It caught up with the competition - but is still trailing behind: not yet out, and already the competition makes it look dated. I don't think we can expect a new release before 2013, and meanwhile, we'll have to support 8 until 2014 at the very least (in theory, we should still support IE 7 and 8; however, the only good thing that came from forced IE 8 installs is that the cumulated shares of IE6/7 is rather low now - but we'll need to retain IE 8, due to XP's popularity).