I downloaded IE9 this morning on my Windows7 machine. It seems pretty good from the 10 minutes I played with it. I didn't have any performance issues out of the box, it seem'd pretty snappy like the first time I used Chrome. Ajax heavy sites, like facebook, were quick and responsive and it has a full "developer tools" suite, like chrome.
I'm still probably going to use Chrome 95% of the time, but I'm not going to go out of my way to discourage people from using IE like I have in the past.
Yet to see if its buggy interpreting/rendering CSS per the IE tradition.
(and at work, we don't have any PC's running anything higher than XP so we can't test. LOL.)