This is a fragment from In defense of Facebook
That’s what Facebook’s ad strategy will work to deliver: social shopping. And I want that. Just as I’m interested in what apps friends install I’m interested in what products they buy, so long as they are willing to tell me, and also what they think of them.
I normally consult my friends when I buy something. I also used to buy something because someone I know and trust bought something (like a digital camera) and raved about it. Social Networks like Facebook just make that kind of consultation and referral easier.
So there is some app idea lurking here. Combine the concept of a virtual circle (gadget freaks is a good example) with product recommendations. It may already be there. Difficult to tell when you have to scan through several thousands of applications.