Dozens of Silicon Valley’s top investors turned out to see the latest crop of companies from Y Combinator, which kicked off the 11th Demo Day at its Mountain View headquarters on Tuesday.

Thirty-six companies showed off what they had built and made their pitches in an “American Idol”-style audition for judges with deep pockets and connections. They each had 2.5 minutes to give presentations. With a mini heat wave hitting Silicon Valley, entrepreneurs could blame their sweaty brows on the weather.

Y Combinator is like a boot camp for entrepreneurs, total immersion in start-up life courtesy of Paul Graham and Jessica Livingston, the brains behind the operation that invests time and money in promising teams and technologies.

The 36 companies made this Demo Day the largest. Graham said nine of the 36 are already profitable.

Among the notables in the audience: prolific angel investors Ron Conway, Aydin Senkut, Ariel Poler, Jeff Clavier and Keith Rabois (who will soon spend his time on Square rather than on investments). Adding to the star power were Ashton Kutcher and wife Demi Moore. Kutcher helped catapult Twitter into the mainstream and invests in technology ventures. But he wasn’t the only one holding court. Moore reeled in entrepreneurs with smart, thoughtful suggestions for new features.