How many feet should drivers keep from cyclists?

If driving in the same direction as the cyclist is riding 5 to 6 feet should be a good safe distance. It be a good idea to slow down till past the cyclist...

Actually, you don't need to slow down as you pass them as long as you are at least 2 feet from them. It can be considered condescending behavior to treat a cyclist in any way different than you would treat them if they are in a car. Remember, they are not helpless, they are not children, they are not fragile, and they need no special considerations that you would not give other drivers.