When I first saw Casino I remember thinking that it contained more f-words than any movie I had seen and someone has done this f-only edit of the film.
Interestingly there is a Wikipedia entry for ‘films that most frequently use the word f**k’
The world record for most uses of the word is a 2005 documentary called (appropriately) Fuck with 824 uses of the word, which works out at 8.86 per minute.
When it comes to feature films, Summer of Sam (1999) follows with 435 and then Nil By Mouth (1997) with 428.
Casino comes in on 398 and then Alpha Dog (2007) with 367.