most thieves who steal from cars know they can't take the car, but the can steal off it,like people on here have said. spoilers,bumpers and so on, and another little tip, leave your glove box open(with nothing in it) happened to a mate a while back someone smashed the window and opened the glove box and nicked all his cd's,
the police did turn up and did say this has happened alot over the last few months,
just have a look what you leave in your glove box? bet some have sat nav's, ipods, cd's and maybe wallet's/purses. all items that can be sold on...
one last thing, another friend had one of the full face steering wheel locks on the her car(the one that covers the full steering wheel) she lost the key to get it off,
I just picked up a load of tools and went to help, 30 seconds later and with a good screwdriver it was off. I was shocked on how easy it was to get off(yes it was only a cheap one from argos) she did take it back and got a exchange(for a better one)