By now, most nonprofits have likely been bombarded with suggestions to hop on the Pinterest craze. So what's it all about, and which organizations can you learn from that have already harnessed the trend?Pinterest, a virtual bulletin board for images and messages, allows users to create and display pin boards of interests -- branding themselves and their ideas through links, pictures, words and ideas.The social media site also hit 11.7 million unique monthly U.S.