writing movie scripts and selling them?

Any of you have experience with script writing?

I took a film class this semester and figured out that I'm pretty good at and enjoy writing scripts for the short films we do in class. An alumni came in a few weeks ago and talked about how he writies scripts and sells them out in hollywood. He said that none of his scripts have actually been made into movies, but production companies still buy them and he gets paid. I'm not interested in doing this as a career, but it seems like a way to make money on the side.