This study of the PC browser market shows some interesting stats.
Janco have been running their study from September 1997, so even if it turns out to be a little off base they've got a lot of context. As of April 2005:
Internet Explorer : 83.07%
Firefox : 10.28%
Mozilla : 3.81%
Netscape : 0.92%
AOL : 0.85%
MSN : 0.67%
Opera : 0.41%
Personally, I use a mixture of (hang on, let me count on my fingers) four browsers for different things on different machines - IE, Firefox, Netscape and Safari (for Mac, obviously) so I don't know where I'd fit into the scheme of things.
