It is a matter of expectations. I've been the Startup School for three times now. I don't go for the talks - I go for the people. The talks certainly have an inspirational bent to them, and most of the info can be gleaned from HN, PG's essays, and a whole bunch of blog posts.
Every Startup School there are a few good talks (Andrew Mason's and Reid Hoffman's were two I liked), plus office hours, which are engaging - but again, these are all uploaded online. I'm not sure how office hours participants are selected, but doing that would be an obvious reason to attend.
The real reason to attend Startup School is to meet a fairly interesting, relatively accomplished, friendly crowd of folks. There's a business bent to the demographic - everyone is interested in startups, but most people I meet are technical. If you really want to, there's the chance to talk to some of the YC partners. Some of the speakers will stick around to answer questions. Last year one of the Airbnb cofounders stayed to answer questions for a while.
To get the most out of it you definitely need to introduce yourself to random people. You certainly shouldn't pull out a laptop. I never sit down with friends because sitting down next to a stranger is a great opportunity to introduce yourself.
Over the past three events I've met a few people I've kept in touch with; that alone makes it worthwhile. It also makes a lot more sense if you're local to the Bay Area - it's a great excuse to meet up with friends in the area.