What I like about it – you don’t have to create an account to use it. Just start emailing text and files (images, video, whatever) to firstname.lastname@example.org and you’ve got a site where it all goes. And they’ve steadily added features. You can, for example, repost all the stuff you email in to Twitter, Facebook, Flickr, Tumblr or wherever.
Today the company is announcing a new product, group blogs. You can add your friends or family’s email addresses to any Posterous site you control, and they can then email stuff in too. It’s useful for families, sports teams, etc. to share photos and video. Once you’ve added those emails, all they have to do to post is send whatever they want to publish to email@example.com. No registration required. An example is here, and see the image below.