I admit I sometimes ride on the sidewalk going towards traffic. In my town there are so many one-way roads that to stay on the street would involve a detour of one and often two or more blocks to the side (b/c of pedestrian malls, adjacent one-ways, and new buildings built across what was a street). If I'm trying to get to another road two blocks ahead, it seems annoying to have to backtrack.
I always go a walking pace around people, but outside of campus there are none. Just going a few blocks this way is a hassle and I will almost always avoid it if possible. Most people here just ride the wrong way up the street in this situation or barrel thru walkers--I ride slow and paranoid. BTW one can legally bike on any non-downtown sidewalk here.