It's my first trip to USA, and it was fantastic!
WWDC 2011's ticket was sold out within 10 hours! and over 5200 attendees from all around the world. And also, Apple announced iCloud, iOS5 and Lion, the next generation of Mac OSX. Besides a lot of technology sessions presented by Apple's engineers, there were also pretty much useful Labs for anyone have some problems on his code. They can ask Apple's engineer directly. Maybe they can meet some guy inside the team which is responsible for the problem. I met one in the UIKit team, and answered a lot of my questions. It's really helpful.
Hope to enjoy WWDC 2012, and hope to be able to USA more freely.