Oh man, I was just about to make this thread : D. I'm pretty excited for the movie, and I agree that the filming style will add a unique brand of excitement, but it also opens up the possibility of a very abrupt ending. The first-person style is supposed to add realism, and in reality, in a situation like that, the camera would eventually run out of battery power, or just get messed up beyond use from being dropped/jostled/hit/whatever. If it does manage to stay intact I somehow doubt that the battery power would really hold out long enough for the conflict of a monster tearing the **** out of NYC to be completely resolved. This would certainly not be a problem for traditionally-filmed movies, but since the director seems to be shooting for realism, I have a very strong feeling that this movie will be ending rather abruptly.
Despite this, I'm sure it's going to be great. At least, I hope it will be- all the buzz and secrecy is certainly getting my hopes up.
EDIT:
YouTube - The official Cloverfield trailer
Trailer that was first shown in theaters. To generate curiosity and publicity, it didn't even give the name of the movie- just the release date.