While I heartily recommend other browsers for the reasons Dean listed, I think you should all be aware of a few points.
1. If you are a webmaster (which probably 99%) of us are – keep in mind that more than 90% of users use IE of some sort, and as much as we wish this weren’t so, it’s not going to change. Therefore, you MUST always keep IE available for checking your websites. I used to keep Netscape/Mozilla/Firefox handy for designing, but it no longer makes any sense and unfortunately never will in the future unless Microsoft is forced to stop shipping IE with Windows.
2. Outlook/Outlook Express is dependent on IE, and unfortunately at least 80% of email users use Outlook. I happen to use Eudora because it is more or less virus/worm-proof but I still have to use Outlook Express for checking the contents of my email.
3. IE is probably the most consistent browser for multi-language purposes – there’s no telling how well Firefox will support users with languages other than English installed on their system.
Sad as it is, I think we’re going to have to live with IE – but as long as you remember to design with IE in mind, shouldn’t be a major problem.