This article (free registration required) in the NYTimes offers some interesting information on the continuing browser wars, and the increasing popularity of non-IE browsers.
I almost never use IE now, preferring Mozilla Firefox, and, more and more, Opera. Firefox has many more features, and the addition of extensions greatly increases functionality (e.g. RSS reader, CSS editing, and many others). Firefox also has better CSS compatibility, but it pales greatly in comparison to Opera, which offers compliance with the latest CSS specs.
It’s a tough choice. I prefer to support open source projects, but Opera seems to be faster and sites that use CSS 2 and above look better. The creator of this blog software prefers Opera, as evidenced by the link to it in the sidebar, so I would suspect that this blog will look better in Opera, and maybe someday look correct only in Opera or a similar browser. The hard thing is, when 95% of the population still uses MSIE, how do you insist that your readers use something else, while trying to include as many as possible?