Jamie Zawinski sells beer, does battle with unix derivatives and rides bicycles. He has posted to the Internet his collected wisdom regarding the latter subject.
"City bikes" and "road bikes" are designed for some Jetsons-slick hypothetical future city that I've never seen. Or maybe for the bike paths in Los Altos or something. Here in real cities, roads are shit, and if you want your wheels and tires to survive curbs and potholes, you need a hybrid. They're a little heavier and a little slower. Are you racing? No? Then you don't care.
We moved to Pittsburgh a few months ago from rural New Mexico, so have been considering the bikes: the city has a similarly compact, hilly landscape to San Franciso, from whence jwz's tips come. Reading this might just have convinced me to give it a whirl.