[telemachos]

What exactly do you mean by "the secret is the service allowing a HUGE forest of porn compilation sites"? That is, does Tumblr actively do something to help porn compilation sites use their service, or do they simply not ban them?

Also, since I often see this mentioned as a difference, does Posterous do something to block porn (however strictly)?

I suppose my real question is "Sure, Tumblr has a lock on the porn market right now, but why?"

[heinel]

http://www.tumblr.com/directory/erotica (NSFW, FYI)

I guess you could argue erotica isn't porn, but yes, they like it. The notion actually extends beyond sexually explicit material, as many popular tumblelogs in the directory has porn or something that alludes to porn in their title even though they have nothing to do with sex.

[Mistone]

porn has always been a great early indicator on the web, and the fact that blogger porn sites have exploded on Tumblr indicates that is usability, and social features are superior.

I'm a big fan of Posterous but the social edge on Tumblr means more traffic and exposure for the blog which what attracts and keeps people on the platform.