Last year, when I interviewed Kimberly Peirce for Stop-Loss, I asked why a relationship played up between Ryan Phillippe's character and Abbie Cornish's in the trailer seemed absent from the final film, not to mention a confrontation between Phillippe and the senator he's driven cross-country to reach coming to a close over the phone and not in person. She explained that about as soon as they had to start editing the film itself, they had to turn over the footage to the promotional department for them to work with simultaneously, and that things don't always match up as a result.
Now, every once in a while, usually in regard to Apatow's oft-tested and whittled-down comedies, absent jokes and alternate takes come as a little surprise. But the year-old teaser for Terminator Salvation capped itself by showing Christian Bale facing off against a robot hiding underwater -- a scene that should appear early on in the film, but doesn't. In Disney/Pixar's Up, our geriatric hero doesn't blow a raspberry as he departs with his house (perhaps for the best), and in 500 Days of Summer, Joseph Gordon-Levitt does not in fact board a bus filled with Zooey Deschanels (certainly for the worst).
What's the most striking occasion you can think of where a scene regularly flaunted in the trailers or TV spots was nowhere to be seen in theaters, and was clearly part of a scene and not a one-off teaser like Pixar themselves so often indulges in?