Tumblr is growing--fast. The site's founder, David Karp posted [3] Quantcast's latest figures [4] on the Tumblr staff blog, saying that its 170 million worldwide visitors had propelled it into the top ten of U.S. blogs. And, like Zuckerberg [5] before him, he pronounced himself "humbled" by the experience.

Tumblr's many gems include this [6] and this [7]. And you just know that this [8] is going to spawn a Tumblr spin-off. When serious news organizations [9] are getting in on the fun, and Tumblr becomes a place to shelter from the storm [10], you can see why it's shooting up the ranks.

[Images from that old chestnut Selleck Waterfall Sandwich [11]]