The Like 'N' Save Coupon Facebook application builds on concept of group buying by allowing brands to offer discounts once a certain number of user like a particular page or offer.  This is how the application works:

• A brand offers a discount or other special offer on a product when a certain number of new fans like their page
• Users like the page in order to participate in the offer and unlock it
• Users are encouraged to share the page with friends via Facebook, Twitter or email to make the deal happen faster
• Users can also subscribe (via email) to get an update once the deal is unlocked

Here is an example of an offer one of our clients recently ran using the Like 'N' Save Coupon Facebook application:

Once the required number of likes is reached, the offer is unlocked (but only to fans), users can still subscribe to receive updates on future offers and they can also share the offer with friends (who will have to become fans in order to take advantage of it).