The thing Tumblr does that's unique is: to join the comment thread you have to have a blog, and your reply goes on your blog (and includes an automatically gene

The thing Tumblr does that's unique is: to join the comment thread you have to have a blog, and your reply goes on your blog (and includes an automatically generated reference to the blogs of each of the other people in the thread). That may sound odd and awkward and in many ways it is, but the consequence is that every conversation connects you to many other people to "follow". And then the posts you get from them on your dash connect you to others. So with Tumblr, it's extremely easy to form "communities" - and to find them.