I also use Firefox only now, except for the rare occasion when some wonky site won't get with the times and only likes IE. That's usually something school-related, though.
Tried Opera a couple of years back. Didn't like it--too weird for me, I guess. Might've just been me being so used to IE at that time, however.
Anyone use Firefox Portable? Carry around all your bookmarks, settings, and whatnot on a flash drive and take everything with you. Great for use at school, work, etc. and for getting around network settings. I use FF Portable and OpenOffice Portable all the time.