Bicyclists in a metropolitan area...
...should follow the same rules of the road as apply to cars.
...should stop at lights, but stop signs are too freqent and too inefficent to stop at.
...should not follow the signals, as they're more like wheeled pedistrians.
...shouldn't be on the road at all. It's too dangerous.
...should consider the signals as guidelines, going case-by-case but generally not following them.
"Should" here is the grander idea, rather than the specific legalities. While different places may vary, assume that the law states that bicycles have all the same rules as cars do, plus one or two bike-specific ones that aren't at debate here.