I've installed the IE7 beta and am quite impressed.... it looks nice, the tabbed browsing works well and some of the rethinking they've done (e.g. hiding some of the menus, etc) is ahead of Firefox.
However, I still don't like the search functionality - I much prefer firefox's "active" find that jumps around the page as you enter the text you're searching for.
I've encountered a few pages that don't load with IE7 (they check for IE6 and will only run on IE6). I found this patch very useful:
The third question contains a link to a registry hack to make it switch between IE7 and IE6 modes.