How many people signup for sites like these, and return rarely or never use any of the registration-enabled features? Are those "real" users as opposed to Face

How many people signup for sites like these, and return rarely or never use any of the registration-enabled features? Are those "real" users as opposed to FacebookApp-enabled users? I add an app in my Facebook. If it's popular enough, every few days I get a bump in my newsfeed from a friend who's actually using the app (albeit within FB). Splash some ads on the landing pages or figure out a freemium model, and all of a sudden it starts looking like a real business (embedded via iframe/fbml!).