Aside from the spyware reason, I really think the best reason to switch to firefox is tabbed browsing. I don't think I could live without it. IE v7 will have tabbed browsing but then you still have the spyware issues. Whenever I use another computer that only has IE I find myself still right clicking the link and looking for the "Open Link in New Tab" button, or middle clicking.

Denon 5803 Denon 3910 Axiom M80ti's, QS8's VP150, EP500's (7.2)