I have to admit that, since I first played with Firefox, IE just hasn't been an option to me. Actually, it's worse than that. I haven't even given IE7 a chance since my love affair with Firefox started, which was before any IE7 beta was out. When it came out, I'd admire from over the shoulders of others, but wouldn't even think twice about downloading it. A bad position to take, I'll admit, but I had it set in my mind that it wouldn't be a revolutionary change, but an evolutionary one. I will say that, if you'd ask my why I prefer Firefox, my quick response would be, "Because it's better." Obviously, not scientific. I never thought about nailing down an exact set of reasons for my Firefox preferences, but the primary was tabbed browsing. I know there are other add-ons that support tabbed browsing in IE, but for some reason, I always felt like IE jujst didn't compare. After working more with Firefox from a dev standpoint, I have to say that the ability to create extensions so easily in Firefox makes it leaps and bounds ahead of IE7. I did switch to IE7 on a new work laptop to give it more of a chance, but I don't use that laptop for dev work, so that was my primary reason. There are so many Firefox extensions that I don't think I could live without as a developer. IE7 is an improvement, but there's still so much that needs to be done. Just like my opinion of Windows, IE needs to be re-architected from the ground-up. Sure, it can survive by growing bit by bit, but a complete change from the ground up, built on .NET would be just the revolutionary change IE needs. Why built on .NET? Two reasons: (1) marketing, duh :-P; and, (2) the future of Windows is going to be built on .NET, so having one of the core features built on .NET now, would simply be a step in the right direction.
For now, I'll keep IE7 around, but I don't think it'll be default on any dev computer. We'll have to see how IE8 pans out.