At least their current iterations, anyway. Turns out a $1 bumpkey – a key whose every notch was cut to its lowest setting can easily open any lock of a given brand. (You need a bumpkey for each brand/kind of lock). Basically, this bumpkey then becomes the master key for all of the locks that use a particular kind of key. Since there are about a dozen kinds of locks on the market, all a thief needs to carry around is a dozen or so bumpkeys, and he can get into your home in less than a minute.
It gets worse: insurance companies don’t reimburse for theft due to bumpkeys, because no damage is done to the door. They can’t determine that someone forced their way into your home, and they’ll simply assume that you left your door open, or are trying to scam them.
Lest you forget, you can open “tough” bicycle U-locks with a BIC pen.