[Legion]

That point is exactly the first thing I thought of when I read the article. How much of Tumblr's traffic is for "photo blogs" of naked girls? Based on what I've observed, probably a good amount.

Not that that traffic is somehow invalid, but I think it makes the comparison a bit more apples-to-oranges.

[zalew]

Not exactly apples to oranges, because that doesn't make the community argument invalid. It's the fun of exploring content on Tumblr that made it possible to grow a network of erotic photoblogs (and not only erotic, check all the 'f*yeahsomething' categories, all kind of lols and such). I didn't bother to check if Posterous' TOS somehow block such content, but still if it was there, currently it's not so easy to find and follow as on Tumblr.

[heinel]

Not exactly apple to orange, but more Facebook to LinkedIn?

A social network's content is its people. I think Tumblr did well targeting the casual crowd. Posterous blogs that I come across, on the other hand, are very "merit-arian," so to speak. Lots of industry focused minds on there that is famous not because of Posterous, but because they are also high in some other circle. In this case, Posterous is only providing them with the tools, with a small Posterous ad attached.

I wouldn't want to see them sacrificing that just to beat Tumblr.