Riding on the Sidewalk
Riding on the sidewalk seems to work in places that have a high density of cyclists. In other words, pedestrians, cyclists and motorists see bikes everywhere and expect them to show up in strange places. If you don't live in an area like this, riding on the sidewalk is not recommended and you should exercise your right to be on the road.
Problem Scenarios
Driveways
Whether it is a residential driveway or a mid-block city alley, legally cars should stop twice, once before the sidewalk, and again at the street. Most don't and if they stop at all, it is at the street -- they plow through the sidewalk.
Pedestrians are moving slow enough to re-act to this, but bikes are usually moving too fast. As such you get hit from the side, or you run into the side of their car.
Crosswalk Slam
Like the sidewalk, cars might not expect you in the cross walk.
Pedestrians
Most sidewalks are designed for pedestrians, not bikes. So they have the right of way. They also don't move in straight lines, and go every which way.