Some sites need it to run (cokemusic, etc), and you always get asked if you want to run it
Firefox uses 3k less memory (23k from 26k from what I can see so far), but it's uglier and IE I can use right from folders on my compy if I want. So far I'm not convinced, and the only plus you've given me so far is that it less less functionality. ;<
(split to topic in techno)