I went to Dragon*Con last weekend. It's huge--more than an order of magnitude bigger than Pengicon, which is the only other sci-fi con that I've been to.
Interesting costumes. Here's someone dressed as Sephiroth in the food court; slightly surreal to have someone carrying a sword in one hand and a Subway sandwich in the other.
A group costume crossing the street.
My favorite, however, was listing to and meeting Peter Beagle, the author of The Last Unicorn.