I just find IE to be... clunky. Having all those windows everywhere and all different sizes, it's just so much neater. I also like the extensions you can install, such as a built in downlaod accelerator and FTP client. The themes are also good (not all of them are horrible and multi-coloured

).
All in all Firefox just seems more professional and when I'm forced to use IE (at school and things) everything's so messy.
(Plus fight against the evil Microsoft corporation :whistle