Oregon law states:

"The driver of a motor vehicle may only pass a person operating a bicycle by driving to the left of the bicycle at a safe distance and returning to the lane of travel once the motor vehicle is safely clear of the overtaken bicycle. For the purposes of this paragraph, a 'safe distance' means a distance that is sufficient to prevent contact with the person operating the bicycle if the person were to fall into the driver’s lane of traffic."

So, about 5-6 feet for most cyclists. Do you want to guess how often this law is obeyed and how often it is enforced? It also doesn't apply if the cyclist is in a bike lane. If the cyclist is in a bike lane, you can buzz them as closely as you like.

Generally, I don't care as long as they don't hit me. If I have to make any unexpected movement, that could be bad--but I shouldn't be making unexpected movements.