I like Batman more than Iron Man so it's only natural I am more excited for The Dark Knight. I thought the Iron Man trailer was just decent- though the visual effects looked amazing, the film has a really superb cast and Kiss Kiss turned me into a RDJ fan so I will most definitely be seeing Iron Man, I am just not anticipating it as much as others.
In the end, the general audience will only get really 'excited' for a film around the time it is out and the gap between Iron Man and The Dark Knight is over two months. In April the GA will be stoked for Iron Man and leading into July they will be anticipating TDK, in the end, I don't believe either will take away from the other.
It's just, on this board, we are all fans who have different preferences and the majority you will find over on the TDK boards, mostly because it is a sequel to a very well received film and features the one villain every fanboy loves. So in that sense, I'd suspect the Iron Man board would be a bit more filled if TDK were not coming out next year, but the hype will always be fluxing.