I remember back when I was a good for nothing kid, we used to steal the occasional bike (btw I have had 3 bikes stolen from me, so I hope karma has caught up with me). Almost any lock wasn't impossible to get through, some just took longer than others. I remember one time taking a bike that was freelocked to itself home, and getting through a krypto u-lock with a metal file. Took about 4 hours, but it worked.

Trust me I don't steal bikes anymore, I think I was 14 at the time...

Phil