Have you ever done the "Find out who viewed your profile" thing on Facebook, and if so, does it really work?

Sometimes I see my friends have done “Find out who viewed your profile” on Facebook and I wonder if it really works. I don’t want to do it if it does not work, because often you have to allow other people to view your information in order to do these apps, and I don’t want to open myself up for something if it does not work.

Have you done it and if so, does it really work?