I visited iPhone Tech Talks on 30th of August. Initially I wasn't thrilled about it and didn't have much expectation . However, I found the show to be very informative and fun. I got to seat and chat with many developers who are actively working on lots of cool iPhone apps and services.
In the beginning of the show, they mentioned that we are in bidirectional NDA (Non Disclosure Agreement) contract. I do not see any secretive information from Apple or iPhone's prospective, but Some developers had some interesting ideas which I'm not going to disclose.
There were bast information given in 5 hours lecture - from Developer's scenario to optimizing for iPhone and how iPhone's safari renders web pages. I tried to gather most of the valuable information and organized in category of guidelines. Hope these helps!!