Both would-be summer champions have an extra bonus for IMAX viewers. Transformers: Revenge of the Fallen has several scenes that were shot on IMAX film (Ala The Dark Knight), and the IMAX version will actually be a few minutes longer. On the other hand, Harry Potter 6 will have a twelve-minute climactic sequence that will be rendered in 3D, just as Order of the Pheonix did. the two films are all-but guaranteed to end up the first and second-highest grossing films of the summer (with Pixar's Up playing a possible spoiler role). If the Paramount sci-fi spectacle and Warner's wizard's tale end up anywhere close to each other in domestic box office, expect cries for an asterisk to be placed in front of the second Transformers's ranking at summer's end.
As a reaction, Warner Bros. could move Harry Potter and the Half-Blood Prince back to Friday the 17th of July (it was moved to Wednesday, July 15th early this year). Or, if it's not too late, Warner could just move Harry Potter 6 to July 24th. So, instead of having to make the fans hold out for two weeks (which is an eternity in this front-loaded opening-weekend driven industry), you now only have one week. Moving to the 29th is impossible since that means that they get less than a month before most kids go back to school, although planting it on August 7th, the day GI Joe: The Rise of Cobra, would be a nice 'up-yours' to Paramount. Any date change at this late period would be a drastic choice and one that could further fan the flames of annoyance amongst the very die-hard Potter fans who would probably see the film in both formats anyway. Plus it would be a signal that Warner Bros. was basically admitting defeat in this unofficial d**k-measuring contest. Still, such a move to July 24th might actually help Warner Bros as the IMAX premiere weekend could cause a much smaller than usual second-weekend drop if the hardcores all go see it for a second time at IMAX theaters.
All this making lemonade out of lemons aside, this is an interesting problem that will have major consequences as IMAX becomes a bigger and more dominant variable in franchise filmmaking. The best case scenario is that this turns out to be similar to the bootlegged copy of X-Men Origins: Wolverine, an 'ohmygod-ohmygod!' story that turned out to be irrelevant when the film opened to $85 million anyway. Truth be told, I can't imagine anyone who was planning on seeing Harry Potter and the Half-Blood Prince on opening weekend deciding not to go because it was only available in 35mm. I'm guessing that this will be more of an 'egg on our face' moment than anything else.