Hey, if you're going to be leaving your bike and/or lock unattended, you need to worry not just about theft but also about vandalism.

Sometimes U-locks get vandalized during the night if they are left on racks - someone trying out their bike theft technique, or just some bored teenagers, who knows why it happens, but if you show up in the morning and your u-lock is broken, you'll have to rely on just your cable. I'd take the u-lock home every night.

I wouldn't leave your helmet with the bike either for the same reason. Some frat boy walks by and thinks it's funny to kick your helmet, and you've got to ride home without. I used to see a lot of bikes locked up on the campus of the school I went to (in NW DC) with missing quick release skewers. I doubt there is a huge market for stolen skewers, I think it was more likely vandalism.

Make sure the parking garage really is the safest place to lock up, too. Check and see if, for example, there isn't a bike rack right outside of the Campus Security office or something.