I also just want to add my .02... While it may be okay to CAUTIOUSLY ride against traffic if you're on the sidewalk and yield to pedestrians, you need to be really careful about riding through crosswalks, especially at busy intersections. I almost crashed into a family on beach cruisers today because they were using the crosswalk to ride up onto the sidewalk rather than walking their bikes. They were going too fast for me to see them in time, but slow enough that I could have easily plowed into them as I was making my right turn. I'm just glad it wasn't a car, because they probably would have gotten hit with how little time vehicles have to react to those kinds of situations.

Long story short, you need to ride where cars (and other cyclists) expect bikes to be: in the bike lane with traffic.