Much has been made of Pinterest’s rapid rise to social media darling and, more importantly, website referral traffic monster.

Indeed, Pinterest’s female-friendly demographic has quickly established the pinboarding platform as a better source of referral traffic than Twitter, Bing and Stumbleupon, and a Shopify study back in May suggested that Pinterest users were more likely to buy and spend twice as much as referrals from Facebook or Twitter.

Not so, says Amazon.

Will Young, director at Zappos Labs, the research arm of Zappos website, which is now a wholly owned subsidiary of Amazon, spoke to Bloomberg about their findings when using their new PinPointing system, a new web tool that finds and suggests Zappos products based on Pinterest posts.

“Social shopping is a total buzzword that people throw around, but I don’t think any big brands have cracked it,” says Young. “When we talk to people and ask what they think is the best social-shopping experience, they say Pinterest, and it’s not even a retailer.”

Zappos discovered that while users were 13 times more likely to share a purchase on Pinterest than on Twitter, posts on Twitter generated the most revenue. And by some distance, too, with Twitter referrals averaging $33.66 per order, more than fifteen times that of Facebook ($2.08 per order) and twenty-five times that of Pinterest (just 75 cents per order). Even combined, Twitter’s purchase power is more than ten times that of these other channels.

“Even if a person has 100,000 followers on Pinterest and she pins something to a board called ‘Stuff I Love,’ that’s not as big a deal as an endorsement tweeted to 10,000 followers,” Young said.

Pinterest recently raised $100 million on a $1.5 billion valuation, largely on its promise as a social shopping phenomenon. While we’ll need a lot more evidence before doing a complete 180 on that position, this data from Amazon does inject a little darkness on Pinterest’s otherwise shining light.

(Source: Bloomberg.)