A photo-sharing service, for example, could create a MySpace-friendly program that allows users to let their friends flip through photos on their own page, instead of leaving the site. Facebook and other Web 2.0 leaders have already gone this route, and the experiment has proven successful. The point of all this, of course, is to keep users in the community. If they don’t ever leave, then they don’t go looking at some other site’s ads.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.