Believe it or not, there's a WebMD article on this and an actual study was done testing the 5 second rule.
Basically the article concludes that there is no consensus on whether it is safe to eat food after it's hit the floor. If it's a dry piece of food or utensil, I rinse it off at home and eat it or with it. If the same thing happens at a restaurant or my office at work, no way, it goes to the garbage. This is me being very unscientific since it is very possible my kitchen floor at home is dirtier than elsewhere, but psychologically I feel better about eating "floor" food if it happens at home.
How's that for a non-answer to this question? :-)