Did you know: "If you post a pin to Pinterest, and it links to an ecommerce site that happens to have an affiliate program, Pinterest modifies the link to add their own affiliate tracking code. If someone clicks through the picture from Pinterest and makes a purchase, Pinterest gets moola."

why is this interesting? most social sites concentrated on getting users first and then had to figure out how to make money. 

http://llsocial.com/2012/02/pinterest-modifying-user-submitted-pins/