It's a blog, website, and an efficient vehicle for publishing material to multiple sites in one quick step.
Besides using Posterous as your own blog or website, there are some great applications for the classroom. A Posterous site could be used as a class blog or website to highlight or archive classroom activities.
It would also be a great way for students to share their creations. By adding student email addresses to the Posterous site (creating a collaborative blog), students can quickly share their learning with the public.
The sign up process is extremely quick, you can customize the look of your page, and posting is incredibly easy. You simply send an email! If you want to include a youtube video, simply add the video URL into the email, and Posterous will recognize it. For any other file types (pictures or mp3s) just attach them to the email and it will be added to your post.
Here is a link to my Posterous site where I created and published this post.