Very often I would see a trailer of a movie that I would like to see. But whenever I was at the movie rental place, I would forget which movies I wanted to see.
Also, I agreed with my girlfriend to limit my visits to the theater to once a month. What a frustration if I just went and two weeks later that one movie came out... That one movie I completely forgot about....
So I created a tag+smartlist 'movies' and whenever I see a movie that I would like to watch I put it in that list. If it is a movie that is not in the theater yet I enter the release date. That way I always know what movie to watch or, in the case of new movies, when to watch it.