A buddy of mine on YouTube asked me this question. I thought I would share the answer with everyone.

According to the iTunes FAQ, the average 2 hour movie will have a file size of 1.5 GB. My buddy's iPod is 8 GB. So he would be able to hold 5 2hr movies. If the movies are shorter in length, which a lot are, he might be able to hold 6 moves.
The answer will vary for everyone depending on the size of the storage capacity of your iPod, MP3 player or cell phone device that plays movies.