50cc's of love
Man, I don't know, I've never ridden one in SF! I think they do OK, though, ther's only a few streets that I think would be a problem, and there are plenty of better alternate routes.
I'm terrified of riding very small scooters- they just feel so wobbly and dangerous! and, man, there's a lot of incredibly bad drivers here, ranging from the dot-commer with cell-phone-ear and Range Rover to Madame Nhu in her S-class slamming on the brakes in the middle of Geary Boulevard to pick up an aluminum can! No place for something without a lot of power, brakes, and stability.
Funny how people who are scared of motorcycles see scooters as somehow safer. Talk about self deception!