Matt Mullenweg should be proud; his giant WordPress.com has reportedly earned him millions. But his blog-platform rival, Tumblr founder David Karp, just surpassed him in one key metric. Mullenweg can blame Brooklyn one-upsmanship.

Like Mullenweg, Karp was a Web entrepreneur as a teenager and is now in his early 20s, creating software through which other people can make money. But while Texas-born Mullenweb has started a series of fights with his tech-industry colleagues, former Bronx Science student Karp has been cuddling his way around Manhattan and Brooklyn.

This sociability has helped Karp exploit Gotham's chattering classes: Tumblr has an estimated one-fifteenth the users of Wordpress.com, but generates about five time as much content, thanks to social networking tools that let its Brooklyn-centric userbase easily quote and snark upon one another's posts. This edge shows up in the sites' public daily posting statistics (Tumblr, then Wordpress):



Meanwhile, Karp, in full bragging mode today, tells us Tumblr averages "five interactions (answers, likes, reblogs, etc.) with each post on average versus 1.5 for Wordpress." That doesn't mean Tumblr is worth $15 million — it has yet to launch its "really sexy" plan to generate actual revenue — but it is an interesting stat, and a testament to the social networking features the snuggly young entrepreneur has built into his site. It's also a pretty solid indication Karp will soon have some additional "interactions" fairly soon, with surly young Mullenweg.

(Top pic: Mullenweg, right, by Jared Greeno; Karp by Zadi Diaz)