I think the reason is that Tumblr is pretty hip and it's geared towards these streams of consciousness - type posts. Most Tumblr blogs seem to consist of rando

I think the reason is that Tumblr is pretty hip and it's geared towards these streams of consciousness - type posts. Most Tumblr blogs seem to consist of random photos posted, maybe a song, or a quote. It's content that is very easy to push out there but is different than Twitter. If you compare it to Posterous, Posterous still feels too much like a regular blogging platform, so they seem to be targeting different markets. Usually whenever a friend tells me that they want to start a blog, I suggest opting for a Tumblr account because they are going to be more likely to stick with it and post more often because of the nature of the content that works well with it.