I'd leave it in the car, and it would cost plenty to replace. Of course, I have insurance that would cover it, less the deductible. On the other hand, it would provide a good chance for getting a new bike!

But seriously, take the wheels off and put it in the car and lock it. Nearly all cars nowdays have alarms that will go off if the door is opened, which they're going to have to do to get the bike out, so it's not really going to be a 'smash and grab' where they just reach in the window and take the iPod or GPS. If the wheels are off and they've got to try to put it back together, it's going to take too much time with the alarm going off. If they don't try to put it together, it's going to be tough to run with.

Bike thefts are crimes of opportunity AND convenience. They'll steal it to go somewhere, but probably not to fence it. The thieves that do this aren't going to have any concept of how much your bike is really worth.

My 2¢, and maybe a little more.