Venture capital is supposed to have dried up. So how did microblogging platform Tumblr pick up $4.5 million in a Series B round late last week? Fred Wilson's Union Square Ventures and new media enthusiasts Spark Capital, who also led Tumblr's $750,000 Series A round a year ago, obviously see something in 22-year-old Tumlbr founder David Karp. We did too.

Karp's wunderkind status (the man's been working full-time on one tech project or another since he dropped out of Bronx Science at 15)—not to mention Tumblr's viral popularity as the liberal elite's platform du jour—have made him something of a media darling, if not fodder for the gossip blogs. But Tumblr's elegant interface and success in building a community are hardly a lucky accident. Indeed features that allowed users to easily post music, links, and photos and "follow" other tumblrs were integral to Karp's vision of creating a page online that users can "live on". Now, Tumblr is now up to 500,000 users and averaging 61 million page view a month, says Karp. Media Memo estimated that Tumblr's investors value the company at around $15 million. Of course, the start-up has yet to break even. And, as the experts have attested, the time to monetize is nigh.

Karp spoke to Inc. about his plans to grow revenue, how exactly the company will spend that $4.5 million, and what it's like to hire to your old boss to work for you. "I was very nervous about the idea of turning into a bigger company. It was one of the things I was freaked out about when we raised money the first time," he says, "Do we have to have a PR person? Do we have to have a weird business arm? They said, 'No, this is so you can keep doing what you're currently doing and not have to worry about where the money's coming from." Sounds downright rosy in this economy.

First up for Tumblr's lastest infusion of cash? New talent.