I've been a non-IE user for a while now, and managed to convert a few people over too. Started off with Mozilla, the switched to Firebird/Firefox. The only that that really bugs me are a) Biggie's menus not working properly, but thats again a code issue that is fixable and b) the odd site that doesn't work, again a minor issue.
Oh, and the Firefox Download Manager sucks badly on low end hardware, it's to do with the way when you add something, it fades in with alpha blending, seems to be better in Win2K than on XP.
Best part is the distinct lack of spyware and browser hijackers I have now.
Good times can be had with the Tabbed Browser Extention, lots more nifty options for tab navigation. I can go through my topic reply notification emails and just go 'click click click' on the links and then switch to FF and have multiple tabs sitting there for quick review. It is a little buggy at times however.
Also grand is Ctrl - and Ctrl + for making fonts smaller or larger. I use + all the time on Biggie. Oh, and type about:config into the address bar for all manner of extra hidden options.