Locks and Keys - Are They All Different?

How unique is the standard door key? Like, if you stick your door key in 500 doors, are you or you statistically going to be able to open some of those? Or is that not enough? Would you have to stick it in 50 thousand doors? I think we'll hear from some folks that maybe answer some of these questions and giveus a little inside, or inside in the world of locks and keys.