It sounds like it's only open to YC founders (and invited guests) based on the following: The speakers were completely open, because they knew they didn't have to worry about someone cherry picking quotes in a blog post to make them look bad.
> but of course also very obvious why this stuff could only be talked about off the record.
Please? It isn't obvious to me :-/
Even when you don't have an NDA stopping you from talking about company X, you still probably want to maintain good will between you and them.
I agree with everyone who said it was a great event. Thanks to Paul, Jessica and everyone at YC for putting it together.