The economy might be imploding, but Tumblr is RICH! The microblogging service/hipster nerve center raised $4.5 million in a round led by Union Square Ventures and Spark Capital, which means the company is worth $15 million, on paper, even though it doesn't make any money, at all. But next year it's going to start selling some "really sexy" add-on features, founder David Karp told All Things Digital. Oddly, Karp's friend/ex-girlfriend Caroline McCarthy hasn't posted this news to her CNET social-network-news blog yet. So we guess the breakup wasn't amicable?