Forbes is out with the latest version of its annual list of the 400 richest Americans and, whatever the gaps or problems with its count, the results are nonetheless illuminating about the social mobility and dynamism of an economy that is as free as America's. From Forbes: "The Forbes 400 gets more meritocratic over time. An all-time high 70% of this year's list are self-made, up from 55% in 1997....The hoodie-clad 27-year-old Zuckerberg is one of 6 club members to get rich from Facebook. Others include newcomers Sean Parker and Jim Breyer, Facebook's venture capitalist, as well as Zuckerberg's former roommate Dustin Moskovitz, whose birthday is eight days after the Facebook chief's, making him America's youngest billionaire. Three other social media mavens made their debuts including LinkedIn's Reid Hoffman, Groupon's Eric Lefkofsky and Zynga's Mark Pincus."