I installed IE9 a couple of weeks ago during one of my regular Windows updates sessions.
There were a coupe of niggly things about it I didn't like, one of them was to do with a change in the interface, minor but not to my liking.
The other thing was an incompatibility problem with some other software, or web site I was interacting with (not this one), but I can't remember what the specific problem was now. It was enough for me to immediately uninstall IE9 and go back to IE8. As for IE9 being faster than IE8, well I didn't notice any significant difference. But to be fair, I hadn't road-tested it for very long.
I also use Firefox for comparison purposes during various surfing sessions. I was using version 3.6.17 until version 4 came out recently, but version 4 is not yet fully compatible with certain browser add-ons for regular software I use, some of them security related. Mozilla state that they will eventually get the add-on compatibility sorted out, but I have reinstalled version 3.6.17 to continue being able to use Firefox fully.
I have also installed Google Chrome, again for test purposes, so if you like a very stripped down browser interface (which is supposed to add extra speed to the browsing experience), then it's probably worth a try.
Personally, I've not noticed a whole lot of difference between Chrome and Firefox.
Laurie.