Keep an eye on it---- what does that mean?

While I was breaking bread with the dead, reading Cicero, and y'know, being a Yale student (how ridiculous that sounds sometimes in the 21st century!), someone asked me, "Can you keep an eye on my computer for me?" I of course replied, "Of course!" However, what does this even entail?

I've often wondered about the Good Samaritan principle in American culture. Do we really look out for each other and make sure that no one steals the other one's stuff? I have a hard time getting someone to hold a door for me, let alone getting someone to make sure some stranger doesn't steal my computer. So the question arises, "Should I even ask? Would they do it anyway?"

Next question: Would someone stop someone from stealing my computer? Would they scream, "Stop thief!" or would they quietly report it to police and take down a composite drawing of the culprit. Would they take responsibility for letting someone take my computer? Or would they say, "It wasn't my responsibility, get a security tracker."

These things I have often times wondered. Hold on, I have to keep my eye on this black HP PC laptop... even though I really have to go get Claire's cake with Misha right now....