The differences are huge. The 770, well, you can write apps for it, for starters. And it can be a remote display to any X app running anywhere. Oh, it has a touchscreen, and hell, it can display a GUI for a program that runs on a supercomputer, with virtually unlimited storage. Use it to order your lunch from a restaurant, either while you're at the restaurant or while you're at home. You can't do that with a PSP.