Yes, mobile compatibility is a big issue, given the flourishing of cheap mobile devices in the developing world. We will definitely do more work to make this a smooth experience on tablets.

And awesome that you mention that -- when I arrived at Khan Academy for my internship on the first day, I was handed a copy of Diamond Age, and told that "Sal wants all the interns to read this". It was an inspiring read for me; especially the notion that part of the goal of real education is to inculcate subversiveness. :)