Hero Complex has confirmed that Marvel Studios is skipping Hall H at the San Diego Comic-Con this year. They could have promoted Marvel's The Avengers there as they did last year, of course, though we assume that Marvel Entertainment will still have a nice presence on the Comic-Con floor.
Much like Disney's John Carter, the studio could be passing on Comic-Con in favor of a presentation at the D23 Expo, taking place in Anaheim, California from August 19 - 21. That has not been confirmed, however.
As far as other comic book movies at the Con, there's no official word that Warner Bros.' The Dark Knight Rises and/or Man of Steel will or will not be there, though we know for sure that Sony's The Amazing Spider-Man will be presenting and that Universal's Cowboys & Aliens will have its world premiere there.