essentially, it's okay to talk about what YOUR company is doing, but it's a no-no to talk about other cos without their permission or off the record things like the dinner talks.
besides, much of how the program works is outlined on the main ycombinator.com website. YC doesn't really micromanage how you present yourself or your co (within ethical boundaries), but provides strong advice[1] that is up to you to follow.
[1]: e.g. don't immediately announce as a YC co as it has press value.
