Time and again I read comments here on HN about new features with the catch that they are only open to users of a certain karma threshold, so as to keep a standard of quality. The "gigs" thread comes to mind. Hey that's cool; I think we can all get behind a little elitism, especially when karma points are being thrown around like something really throwable.
So, I'm proposing the Mecca of elitist social networking sites. Any page created can be assigned karma thresholds for viewing, commenting, voting, whatever. To place a widget onto your page, you must meet its karma requirements. Want to view my new page? You must be this karmic to enter. Want to read my latest hack? That will cost you 1 point deposited to my account.
But those were not very good examples; there isn't any point in restricting your audience. But for abilities such as embedding pictures and video that can be abused, the karma requirements would be set very high by the karmic gods themselves (the top 100 users).