I managed to make it through TPM and AOTC, but I left during ROTS. I went to see it expecting it to be bad (a friend had two free tickets). Unfortunately I'd seen most of it (I made it to the lava planet fight thingee) before I decided I'd paid too much.
EDIT: Actually I did pretend to go to the bathroom during AOTC. So I left the theatre and hung out in the lobby for a bit, then took a deep breath and went back in after I felt I could take some more. Does that count as walking out?