I just installed IE 9 beta, and as first feedback I have to say it’s very quick to install it; quicker than IE 8.
Another feedback, displaying a web site is also quicker than with previous IE version (and also lot of others, to not say all, browser).
As part of the new features, you will see a ‘ribbon’ at the bottom of your windows to help you browsing quicker by disabling add-on; in fact IE will inform you which add-on is causing trouble and you will be able to disable it or not.
So enjoy with the beta