Mr. Massoumi, who conceived of ZocDoc after rupturing an eardrum on a flight.

ZocDoc just raised its $50 million Series Cool from DST Global, making the online booking and review site for doctors' appointments the first New York investment by Facebook/Twitter/Zynga/Groupon investor DST Global.

ZocDoc offers five million available appointments across nine major metropolitan areas and "is in the midst of a nationwide rollout," a DST rep said in an email. ZocDoc says it books about 700,000 appointments a month; the start-up was also named the best place to work in New York by Crain's.

ZocDoc gets revenue from physicians and other healthcare providers who pay $250 a month to be listed and book appointments through ZocDoc. "By giving patients access to real-time doctor availability, ZocDoc is bringing radical new efficiency to the healthcare system. The service lists a ‘hidden supply’ of appointment times that would have otherwise gone to waste, including the 10 to 20 percent of appointments made available by last-minute patient cancellations," the rep wrote.

"Our aspiration is to be as big as Google or Microsoft. Our market is that big. We have the potential to be that big. It’s just a matter of how long it takes us to get there,” CEO Cyrus Massoumi said in an April interview with the NYC-based start-up blog Founded. What, $50 million ain't cool enough for you, Cyrus?