I caught The Dark Knight at IMAX, and it was so worth the wait (waited in line for an hour, on a weeknight!). I've watched a few movie at the Boeing IMAX Theater at the Pacific Science Center a few times now, and each time I come back amazed at the infinitely better movie-watching experience that the theatre provides. Select scenes of The Dark Knight were shot for IMAX (pretty much all cityscape scenes in Gotham City and Hong Kong) and they were just stunning. Too bad there were no real 3D scenes, like there were in Harry Potter and The Order of the Phoenix. I really need to catch more movies at IMAX - its likely the long lines that put me off, but I need to keep reminding myself that they're totally worth it.
If you have a choice to watch a movie @ IMAX or at your neighborhood multiplex, do yourself a favor and pick the IMAX experience.