Locksmiths love WD-40.
People spray it into the locks then a few days later the lock stops working. Especially in a dusty atmosphere. I had a locksmith tell me one time that if it wasn't for people using WD in their locks he'd loose half his business. He was being facetious of course but he was making a point. Never never spray WD in a padlock, door lock, ignition switch or any type of keyed mechanism. You'll regret it.
Like Map said, it has its uses but locks aren't one of them.
Oh, and sawdust probably predates bananas