Depends on the situation. I ride on the sidewalk only where there is no safe spot on the street. Taking the lane on a street where the flow is over 35 mph is not something I would do lightly, and not with out being damn sure the car behind sees me.

Sidewalks have their own inherent dangers, but if you are aware of them, and ride accordingly, it is manageable, but if done safely, usually much slower. If they are heavily traveled by pedestrians, riding the sidewalk is also rude, but this is Southern California, and there are more joggers on the MUP's than walkers on sidewalks.