Yeah, I think they're designed for different niches.
I use Posterous as my platform for publishing content that's text-based - I really like using my email client as a UI, and it makes it easy to post from anywhere. It's also dead simple (once it's set up) for non-technical users to run a blog using that interface, and would be of great use (I imagine) in a situation where bandwidth is at a premium, like in remote environments where all you've got is an expensive satellite uplink.
Tumblr, on the other hand, is very much more of a social/media blog platform. It's got that feature where you can re-blog something and it automatically links back to others who have done that, among other neat features. I'm also a big fan of its bookmarklet for sharing links and media, and while it's fine at doing text, it's in no way exceptional.
In short, I consider Posterous to be a very well-executed text-centered longer-form blogging system, whereas Tumblr is more optimzed for media/content sharing and short-form text - although both would work for either niche.
I use Posterous as my platform for publishing content that's text-based - I really like using my email client as a UI, and it makes it easy to post from anywhere. It's also dead simple (once it's set up) for non-technical users to run a blog using that interface, and would be of great use (I imagine) in a situation where bandwidth is at a premium, like in remote environments where all you've got is an expensive satellite uplink.
Tumblr, on the other hand, is very much more of a social/media blog platform. It's got that feature where you can re-blog something and it automatically links back to others who have done that, among other neat features. I'm also a big fan of its bookmarklet for sharing links and media, and while it's fine at doing text, it's in no way exceptional.
In short, I consider Posterous to be a very well-executed text-centered longer-form blogging system, whereas Tumblr is more optimzed for media/content sharing and short-form text - although both would work for either niche.