I wrote a blog post about why I joined (not started) the scuttlebutt project: staltz.com/my-last-day-and-my-first-day.html
Basically the motivation is panic: we are losing our internet. It's not ours anymore, and it's becoming something else. It's time to build something else, from ground up, which guarantees it belongs to us. No one owns the oxygen in our planet, it's for free and belongs to everyone. So is interpersonal-communication, it should be for free and belong to whoever is speaking, only. Facebook is a threat to that, today and in the future.
and why has the focus not been on mobile and usability? Do you see any possibility of scuttlebut being mainstream, and not just being used by esoteric techies?
I joined the project to bring it to mobile and with a focus on good usability. We have plans for bringing it mainstream, it's not going to be just for techies, for sure.