When I volunteered to lead a study group for my physics class, I wasn't reallly expecting anyone to show up. Not a single person asked me for help last semester, even though it was obvious by my test scores that I was significantly ahead of the curve. So I was planning on essentially having a study hall after class each day where I could get other work done. Surprisingly, I have had several customers and at least one new person each day.
I am becoming more and more certain that I love teaching. It gives me such a high when a student leaves the room feeling more confident about the material than when they arrived. In many ways, they are helping me more than I'm helping them.