An annual ranking by this site called WalkScore, which provides detailed, neighborhood-by-neighborhood scores of various cities based on their walkability and access to public transit, has put San Francisco as the second most walkable city in the nation (behind New York). Surprisingly, Oakland makes the top 10 as well, ranking at number 10.
We will disclose that we lived in Oakland once, and it's really not that walkable! Sure, there's a downtown (where hardly anyone goes if they don't work there), and there are a few neighborhoods like Rockridge and Grand Lake that are somewhat walkable. But we didn't know anyone who lived there who didn't have a car -- compared to S.F. where a great many of our friends are carless. We suppose that there aren't a lot of car-free folks in any of the other top-ranked cities either (Boston, Philly, Minneapolis, Seattle), but still, we must say Oakland's a bit of a stretch... especially considering how far apart the BART stops are, and how desolate many of the densest neighborhoods are after 6 p.m. Just sayin.