Pinterest's promise lies in its apparently unique connection to online shopping, but so far the numbers don't conclusively prove that the social network drives incredible sales. The latest statistic comes from Zappos, which has created a site called PinPointing that recommends purchases based on Pinterest pins. According to Bloomberg's Danielle Kucera, the data found that Pinterest facilitates buying, but only to a relatively unimpressive extent. An average Pinterest purchase came out to $.75 on average, compared to $2.08 per order from Facebook referrals and $33.66 from Twitter. Beyond Pinterest's quick rise to the third largest social network on the Internet, it got itself a $1.5 billion valuation last May because (unlike Facebook) its fashion oriented Pinboards push people to online retailers, which best case scenario would lead to sales. But, as we can see above, just because Pinterest encourages virtual window shopping, it doesn't necessarily lead to buying.

To be fair, the numbers aren't totally conclusive on the Pinterest money-making equation. The Zappos study was just a single case, which might be the exception, not the rule. With a complete opposite conclusion, Bottica, a jewelry and accessories site, reported that Pinterest users spend more than twice as much as those from Facebook, per Econsultancy.com. And on a larger scale: looking at 25,000 retail partners, Shopify found that shoppers from Pinterest bought more on average than those from other social networks. The data showed that an average order from Pinterest was $80, double the average order from Facebook. 

The statistical disparity might have something to do with the kind of referrals these sites are getting from Pinterest. Because of the way the pinning and following system works, the social network introduces people to new sites more than other social networks. When it comes to those first timers, Pinterest gets people to buy more than Facebook or Twitter, as the chart below from Venture Beat's Jeffrey Zeller shows. 

Not taking this into account, however, Pinterest loses much of its edge, as this other chart from Zeller shows. Though, it is still the most powerful driver of buying. 

And even if people don't spend more money, the stats show that people coming from Pinterest were more likely to purchase. Bottica found Pinterest "assisted" 10 percent of sales, compared to Facebook's 7. And, Shopify found that pin loving shoppers were 10 percent more likely to buy than those from other networks. Pinterest clearly gets people to shop. Another survey by Bizrate Insights found that 32 percent of North American shoppers coming through Pins purchased after perusing. Though, a Venture Beat analysis, looking at 40 sites, found even in that department  it still lags behind Facebook. At least as of April last year, Pinterest made up 17.4 percent of all social media related revenue for e-purchases. That is "quickly gaining on Facebook," writes Venture Beat's Jeffery Zwelling. But, to give an idea of how much catching up Pinterest has to do: the more established social network had 86 percent of that market last year.  

This matters particularly for Pinterest because its worth comes not from its big audience -- as we've seen with Facebook that doesn't guarantee anything -- but in its ability to drive sales. At least some of those millions of people are going to an online store and clicking to buy. It's just not clear how much better Pinterest is at this when compared to other social networks.