asking a stranger to watch your stuff

[eviljeff]

background:
I go to a law school with about 1500 students. There are many places to study, most of which require key-card access. Some of these rooms are usually well-populated and some of are usually empty. Most people just leave their laptops and bags when they go to take a bathroom break or print something out. Sometimes for even longer periods like a meal break. (side note: I always take my stuff with me)

situation:
I'm studying in one of these large key-carded rooms late at night. There is one other person in there. She is studying on the other side of the room. She comes over and asks me to watch her laptop and such for about 20 min. What I started to think about while she was gone was whether or not her stuff was actually more likely to get jacked given that she told me she would be gone for a considerable period. If I did jack her stuff she could easily have discovered who I am given that I'm in the building every day and all law students' pictures are in the facebook. However, she doesn't know that I'm a law student. Students from other areas of the university (and possibly other schools as well) study in the law school. True, there is key card access, but it's pretty easy to just follow someone in.

focus:
When have you asked a stranger to watch your things? What other situations can you think of where you might do so? Would you be more likely to if there were a lot of people around or just one? What is the most valuable thing you would ask a stranger to watch?