i've been using Safari on my powerbook at home for quite awhile now, and i haven't noticed any problems with it as far as going to sites that are more than likely IE compatible
i have a feeling that Apple worked their browser closer to IE's compatibility since most developers develop for IE, and if Apple wanted a good workable product, they knew they needed to do something, not like IE persay, but that works and acts like it so people wouldn't be upset that IE is gone
i personally love Safari, it hauls arse compared to the Mac IE and PC IE, IMHO