I attended last year's startup school. It is absolutely not an advertisement for YC. It's basically a bunch of people who are deeply involved in the startup world offering their advice on how to start up.

If you are contemplating a startup or you're already doing a startup I would say it's worth attending. Outside of the interesting talks (which will most likely find their way online anyways), it's a great opportunity to talk to other like-minded people and hear about what sort of stuff they're working on.