I've been running IE7 for a while now and there's two things that I never would have thought of as being a big deal that I've gotten really fond of. Well, actually three, but the third is tabbed-browsing which is kind of old news.
First, I'm starting to really dig the new search provider bar. It allows me to add a bunch of different providers and then search their site without having to navigate there first, mostly eliminating the need to install random toolbars. Naturally, you've got MSN Search, Google, etc., but I've started using things like Weather.com. Just type in my zipcode, and up comes the weather. eBay and Amazon are great too. It's super easy to get used to - FireFox has had this for a while but hopefully with OpenSearch more and more sites will support it. I'll admit, I'm not sure how FireFox is doing it...there's not much info about how it works.
Second, the new Favorites management UI is really great. It took a little getting used to but now I use it all the time. I almost never used-the old menu-based setup and now I've actually invested in organizing my favorites and regularlly using them. Having it merged in with my Feeds is nice too. I've started using IE pretty much exclusively as my RSS reader.