How would you monetize a social media site?
tortilla: My buddy runs a social networking site for a niche market and they run a freemium model along with ads.  The one mistake they made was charging too little as the difference between charging $6/month and $15/month is not as great as they expected (they have 2 levels of paid subs).  The bigger hurdle is just getting the user to pull their credit card out in the first place.  So don't be afraid to charge a fair amount, if your site offers good value.