Happy browsing... until you restart your computer.
Not sure if this happens to everybody, but for me, every time I restart my computer IE resets itself as the default browser. I have to reset it to Safari after each restart. (Entourage does the same thing, making itself the default mail program.)
Also, every time I start IE (I need it for some pages), it asks me if I want to set it to be my default browser--no matter how many times I check "don't ask me again".