Today marked the fourth year of Y Combinator’s startup school, and judging by the overflowing auditorium that persisted throughout the event, it was a runaway success. A crowd of over 650 developers, writers, and entrepreneurs packed Stanford’s Kresge Auditorium for a chance to pick the minds of tech-industry greats. The annual event gives members of the startup community, particularly technically-minded ‘hackers’, a chance to learn and ask questions about venture capital, IP law, and other aspects of the startup process.

This year’s speakers: Sam Altman (Loopt), Marc Andreesesen (Ning, Netscape, Mosaic), Jeff Bezos (Amazon), Paul Buchheit (FriendFeed, Gmail), Paul Graham (Y Combinator), David Heinemeier Hansson (37Signals, Rails), David Lawee (Google, Xfire), Jack Sheridan (Wilson Sonsini Goodrich & Rosati), Greg McAdoo (Sequoia), Peter Norvig (Google), and our own Michael Arrington (TechCrunch).

Highlights:

-A young man named Brandt who couldn’t understand why Sequoia Capital and other top VCs refused to fund his adult website. Sequoia’s Greg McAdoo responded that he had a hard time picturing a porn site’s IPO.

-David Hansson’s presentation, which was easily the most entertaining of the afternoon. Hansson, who created Ruby on Rails and is a partner at 37signals, espoused a pay-for-use model that stands in stark contrast to the free services that seem to define Web 2.0. As he mentioned, this model hasn’t worked for everyone…

-Jeff Bezos dodging a question on Google App Engine, explaining that his company “doesn’t like to talk about other companies.”

-Paul Buchheit’s joking admission that he spent his last few months at Google “basically doing nothing.”

A video of the entire event can be found at Justin.tv.

The slides plus video can also be found over at Omnisio.