I've been playing with browsers at work recently. I installed IE 7 on my backup machine, and on my main machine I installed Firefox 2 alongside Firefox 1.5 in a setup that allows them to run side by side.
IE 7 first thoughts were bleh. There isn't anything there to make me switch back. To me the UI isn't better than Firefox, and it isn't more useable. It really isn't all that special. Nothing jumped out at me that was a key feature.
Read the IE7 feature set here. All of their "Makes every day tasks easier" are things that Firefox has been doing for a while. Enahnced security with IE7? I don't feel it. Improved platform? I would agree with that, but it still feels like a catch up to me.
Now with Firefox 2 I found something to get excited about within 10 minutes of using it. Read their release notes here. Phishing protection, session management builtin, better handling of web feeds, inline spell checking (that is awesome), and more.
I don't forsee using a browser to manage my web feeds any time soon, but with Firefox 2 I can set which application I want it to use to handle my feeds. I changed the setting to RSS Bandit, and now when I encounter a new site, and Firefox informs me that it has a feed, I click the icon, and RSS Bandit pops up with the add feed already in progress. If there are multiple feeds on the site, there is a drop down to choose the feed I want. Very, very handy. I like it.
The inline spell checking is very handy. It works like a spell checker should, and I can modify the dictionary to suit my needs.
Even more astounding, almost all of my Firefox 1.5 extensions worked with Firefox 2. The ones that didn't, were on my nice-to-have list, so I can live without them for a while.
Verdict: I will keep Firefox 2, and still won't use IE very much.