Tumblr founder David Karp plans to make money off his microblogging platform — the one used by Julia Allison as well as dirtier, more creative types mostly found in San Francisco's Mission District and Brooklyn's Williamsburg — by creating a front page kind of like Digg's. Except on Tumblr Radar, a video, post or image's popularity will be determined by how many times its "reblogged." The idea is to help users discover other Tumblr blogs while serving them brand ads. Karp was overheard talking to former DoubleClick founder Kevin Ryan about the prospect last week. Karp has told us this front page will end up looking like a cross between Apple's iTunes store and Ffffound.com. Thanks to a rule-breaking beta tester, we won't have to wait to find out if that's true. Here's a leaked screenshot of Tumblr Radar:

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