Pinterest may be facing user backlash in the wake of the news that the company has been quietly making money off of its customer base.  Josh Davis at LLSocial.com uncovered the when a pin is posted to the site and it links to an ecommerce site with 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 paid." The site is using a third-party service called Skimlinks.

Even if majority of Pinterest users does not have a problem with this, writes Search Engine Land, "it is a questionable decision from both a business and ethical standpoint to not disclose this fact to Pinterest users. If Pinterest wants to regain the trust of its users, they should fully disclose the details of the affiliate program and issue a statement as soon as possible."

A Growing Phenomenon

The news could not have come at a worst time for Pinterest. Despite being an invite-only site that uses virtually no marketing, it has become something of a social media phenomenon.  Pinterest now drives more referral traffic (3.6%) than YouTube (1.05%), Google+ (0.22%), and LinkedIn (0.2%) combined, according to Shareaholic’s January 2012 Referral Traffic Report. Pinterest grew 44% from 2.5% of referral traffic in December 2011, after owning just 0.17% of the traffic in July 2011.