I was pondering making a tumblr knockoff a few days ago. It would be called bumblr and its gimmick would be that the only way you can find other people's pages is by pressing a "bumble" button that randomly takes you to one. It would form connections between other humans and I imagine it would eventually take over facebook and actual tumblr.
Bumblr.com is even unregistered as far as I can tell. What a great opportunity to establish the next big thing.