For what it's worth about not being able to see it IMAX due to the sell outs so far in advance, this popped up in a paragraph over at Anne Thompson's blog on Variety:
Finally, I would have preferred to see The Dark Knight in 35 mm, not IMAX. (I will go see it again when it opens July 18.) While the sequences that were shot with giant cameras were stunning at the IMAX venue--especially the deep detailed helicopter shots over Gotham and the amazing car/truck chase filmed in Chicago's freeway tunnels--I found the movie overwhelming.
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When I saw the film it was also in standard 35mm and it was just as engrossing, that said, IMAX would've been great, but 35mm was suffice.