Facebook is adding a new Timeline section to highlight the groups to which you belong. The new Groups section will appear on the About tab on the new Timeline.
Facebook launched their new Timeline design, a one-column format with more focus on interests, in early March. The main Timeline page got a facelift, streamlining stories and moving other information and activities to the left-hand side. More relevant to this story, the About section also got retooled. Each interest now has its own section, and you can also add custom apps like Instagram or Foursquare activity if you so choose.
Facebook is still in the process of rolling out the new Timeline.
Anyway, Facebook tells Inside Facebook that the new Groups section on your Timeline will only show the "open" groups that you belong to. Both closed and secret groups should be hidden from the new panel, something that should please those concerned with privacy in light of Facebook's problems with Groups visibility.
Groups will join individual boxes for your friends, photos, music, movies, Tv shows, books, games, likes, and app activity on the About section on your Timeline. Facebook just unveiled the new Games section a couple of weeks ago.