I would only consider using IE if it was the only browser available.
I find it (when I have to use someone else's computer) terribly unweildy, slow, and hard to use compared to Opera.
Opera has 'mouse gestures' which lets you flick back & forth through pages extrememly quickly, and if on the rare chance it might crash it won't bring the whole computer down like IE can. It'll also pick right back up from where it left off.
I prefer Opera 6.05 over the latest 7.1 though, it seems to run a little better. Still testing though ...