In a somewhat ironic twist, Internet criminals who make their living by exploiting the machines of others (typically for extortion--the threat of a botnet looming down on some sites is enough to make them pay protection money) don't use MSIE. The breakdown is something to the effect of: 50% use Firefox, 25% use Opera.
http://it.slashdot.org/article.pl?sid=09/08/21/2119253
The link in the /. story does have an ad in it before you can get there. It's a bit humorous, especially the tag "becausetheyknow."