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.