Very rarely nowadays.
When I was younger I did. For instance, I've seen ALL THAT JAZZ about 15 times. My best friend was obsessed with Roy Scheider at the time and he saw it 50!! times and dragged me along for 15 of those. I do love the film though, btw.
The only recent film I saw more than once in the theatre was A HISTORY OF VIOLENCE, and that was because I had a friend that really wanted to see it with me after I'd already gone. I was glad to in that case because I thought it was a great movie.
Now, especially with dvd and the fast turnaround on theatrical to disc I see no reason to. If I like the film enough, I'll buy the dvd (and usually get bonus material, right?). I also generally dislike the theatre experience (commercials, loudmouths, etc ad nauseum).