With Google+ they are trying to offer a new product which has the best features from Facebook, Twitter baked into it from day one topped with some kick-ass features like Hangouts, Huddle, Circles and a slick intuitive interface.
Yeah right now mostly techies are using but once it becomes open to all, a lot of folks are sure to join in. Even if they don't want to, the black toolbar on top of their gmail and other google products will eventually draw them to try Google+. It might be quite difficult to make 750M Facebook users to migrate, but Google+ can provide a significant competition to Facebook and Twitter as well.
After about 30-60 minutes of using it once, just about anyone should be able to know how to use it. I know people who kept asking me how to use Facebook days after setting them up.
Yes, Facebook is common and everyone has it, but that does not mean its interface is easier to use than Google+. Quite the opposite. It has a mediocre interface at best, and it's slow compared to Google+.
The reason it's used by techies mostly right now, is because most of the initial users that got invites were techies, and they invited mostly other techie guys. It has nothing to do with the interface or the product itself.