Defcon was quite cool.
I got the impression that Americans have an alcohol problem, though. People went way overboard at Defcon, as though they were not permitted to drink at home.
And people in the US apparently earn way too much money. Everyone acted like he was the Chosen One. But it was very funny nonetheless. The friend who travelled with me even won a Sparc IPX. We were quite worried how the airport security people would react (they normally want you to "switch it on" before their eyes).
I visited Usenix Security, too, and I was impressed by the quality of the papers and talks there.