For myself usually once is enough, I've seen Star Trek twice now and will end up seeing it at least twice more going by my current plans.
The only film i've seen more is Titanic which I confess I saw 5 times in 1998. Hey, I've been into the Titanic story since I was a kid!!
Films I've seen twice though (that I remember so far) are - Star Trek: First Contact, Scream, Indiana Jones and the Kingdom of the Crystal Skull, The Ring, and The Boat that Rocked.
The only film I've ever walked out of was Dreamcatcher in 2003. After about 45mins I just couldn't stomach the mess that film was and my friend and I left.
The most I know of anyone seeing a film was that same friend of mine, who in 1994 literally went insane for The Lion King and saw it 24 times (with ticket stubbs to prove it!)
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist