Move over Facebook, Twitter and Google+. Another social media site is stepping up as a valuable marketing tool for businesses.Pinterest, an online bulletin board for your favorite images, launched in 2010 and is already experiencing wild growth. The site registered more than 7 million unique visitors in December, up from 1.6 million in September. And it's driving more traffic to company websites and blogs than YouTube, Google+ and LinkedIn combined, according to a recent report from Cambridge, Mass.-based content-sharing site Shareaholic.
