Just recently Facebook started a limited trial within their office and at select US college campuses, where users could gift virtual currency to each other for use in the Facebook gift store.  The idea seems to be centered around rewarding your friends for posting interesting content so is linked to the "comment" and "like" buttons in the news feed. And now it looks as if the experiment has been widened to augment branded virtual gift campaigns like this effort from Mars. When you visit say the Snickers fanpage, click through to the Gifts tab and up comes a free branded virtual chocolate bar that you can gift to your friends.  But the free gift also comes with a virtual gift certificate of 10 Facebook credits which will go to your Facebook Gift Store account - so you can keep spreading the love! According to Inside Facebook,

Branded virtual gifts are one of the more promising new forms of online advertising in social environments, because studies show they're often a form of advertising that people actually like to receive.

The addition of credit gifting is only going to strengthen that proposition.