"Branching" sounds interesting. I've thought about my ThoughtStreams (my streams?) as a graph almost since the start. I found myself writing on ThoughtStreams the same way I talk to a friend or think about a problem: there are digressions, forks, and often threads come together. I'm hopeful the release of branching will make it possible to do a lot of those.
That does make me wonder, though, is the "stream" the first class citizen in a branch-enabled world, or is it the "thought"? Maybe it's only a matter of rendering, but I sort of hope there's a way to see the world as a series of branching conversations.