The idea of an online magazine with content that can be customized by its readers has been around for years. The execution of that idea, though, has produced less than stellar results. That may be about to change with a new free application released this week for the iPad called “Flipboard.” Flipboard combines information from Facebook and Twitter to create a personalized magazine on the iPad — a “social” magazine, as the service calls it. What really distinguishes Flipboard from other efforts in this vein is the stylish way it’s able lay out that information.