I am still excited about IE 9, even after using it.
On the surface it is a fast and capable browser. It is strange to double-click on the blue "E" and have web pages perform like they do when starting Firefox or Chrome. The performance probably suffers on my computer because I have a very old video card and am using XP drivers rather than official Vista drivers, but that only would explain the graphics artifacts I occasionally see.
While all the demos I tried worked on Firefox and Chrome (with the exception of the real time capabilities of Smoothie Charts - http://smoothiecharts.org/, where Firefox would not draw the charts real time ), only a few worked on IE 9. I also tried out a HTML 5 support test web page ( http://www.html5test.com/ ) where IE 9 scored 96/300 and Chrome scored 217/300 and Firefox 139/300 -- also linked on WebAppers.
In all, IE 9 Beta is amazing by Microsoft standards, but basically a bit below average compared to the other modern browsers. Hopefully the IE 9 gets additional speed and HTML 5 support as time goes on. Back with IE 4 and 5 Microsoft set the standard for web browsers, and they still do.. as the lowest level browser they are the baseline for what components you can count on all users having access to. The only remaining trick is to get all the XP users out there to Windows 7 so they can install IE 9 as it is not avalable for anything below Vista.
(Speel chek is stil missing, so becaue I am writing this in IE 9 Beta you are allowed to keep any misspellings you have noticeed)