Heh... "90 degree summers" is mild. More like 105. Summer is brutal, though I actually haven't found it all that humid. That said, we were throwing pool parties in November while my friends in SF were walking around in coats.

Sept-Nov is nice in SF, but otherwise it was too cold and windy for me. I lived in soma, though -- if I were to do it again, I think I'd live in the Haight, mission, pac heights or the marina and I'd probably have a different experience. The variance between neighborhoods in terms of climate and culture seems to be greater in SF than I've found in Austin.