Today Windows Update suggested I install IE9 RC, so I did, and tried it out. Hence my earlier comment about modernizr.
I'm not a fan of the interface. Many of the buttons are in the wrong places. Why is the Home (and favorites) button way over to the right, away from the other navigation buttons? Ditto with Reload and Stop loading. All the navigation buttons should be near each other, IMO. I also don't like having the tabs and the address bar in the same vertical space. I open a lot of tabs, and they get cramped way too much when most of the room is taken up with the address bar.
Also, an extension shows up in a toolbar which takes up an entire horizontal row all by itself. Why? This wastes all the space that was saved from putting the address bar up with the tabs. I prefer like the way Chrome handles it with a small icon for extensions in the same area as the address bar.