"There's nothing better than receiving an email or phone call from someone saying their evening was better because of our meals," says the 26-year-old cofounder of Scratch.

5 seconds. That's about how long website creators have to capture a visitor's attention and convince them to stick around. Fabian Stelzer used his training in neuroscience to help create a tool for web designers that analyzes just how sticky their page is likely to be.

"Don't try and figure out what the world needs. Figure out what makes you alive, and do that--because that's exactly what the world needs," says Dave Radparvar.

Ljung put his life on hold to build his own cloud focused on sound creators instead of consumers--a Flickr for music.

Aaron Levie, co-founder of cloud company Box.net, talks Steve Jobs, Mark Cuban, dropping out of college, and his once-in-a-lifetime opportunity.