Yep. It was Batman, The Dark Knight, but my wife had no interest in it and we didn't have much money at the time. With great shame, I share the fact that I ditched work at the pizza joint I was working in at the time and went to the movie. Being alone at the theater was, as msorensson said, fascinating...minus the guilt, of course. I'd like to try it again sometime without sneaking around about it.
I like alone time.