More and more retailers are adopting Facebook “Like” button. Facebook Like button provides an easy mechanism to share content you like with your friends on Facebook. Retailers like Best Buy, Sears, eBay are actively using Like button on their websites.

In recent weeks, a growing array of shopping sites have placed "Like" buttons on their pages, too, including those of eBay Inc., Best Buy Inc. and Gilt Groupe Inc., expanding Facebook's influence into a $140 billion industry in the U.S. that drives both online advertising and a growing portion of retail sales.

For e-commerce sites, adding a "Like" button lets shoppers quickly share a product or deal with their Facebook connections, potentially encouraging them to buy the product themselves.

"Customers are looking to other friends in their social network to figure out what product is right to buy," said Tracy Benson, senior director of mobility customer solutions at Best Buy.

While the Like button can increase traffic, there is not established case study/research which shows increase in conversions for traffic originating out of Like button.

Daniel Mandell, a director of business development at Wenner Media, the owner of Us Magazine, said the celebrity website soon will roll out the Facebook "Like" button after years of allowing its visitors to share content on Facebook through other sharing buttons.

Visitors from Facebook are valuable because they "are an extremely engaged audience," spending an average of three minutes on the US site, about 20% higher than visitors from search engines, he said.

For shopping sites, though, the key measure of success is sales, not traffic. After Gilt introduced "Like" onto its "flash sales" pages at the end of June, the site saw a 50% leap in sales coming from Facebook after the first week. "We are watching to see if it continues, beyond an initial bump because it is new," said Jag Bath, the company's vice president of product management.

"Everyone is hoping that the endorsement of a 'Like' button will be the thing that gets consumers from browsing to actually buying," said Fiona Dias, executive vice president of strategy and marketing at GSI Commerce Inc., which runs about 100 retail websites. But among her clients who have implemented "Like," there has been no direct correlation between top-selling and most-"Liked" items.

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eMarketer reported last month a good increase in Retailers adopting Facebook Like button and other Social Plugins.

Mashable ran a story few days back showing How Online Retailers Can Leverage Facebook’s Open Graph. Good Read.