Move over ad Twitter, here comes ad Pinterest. The social networking service, which allows users to "pin" items of interest (get it?) to digital boards, began offering personalized recommendations back in July. Now, it's taking the approach one step further with plans to introduce promoted pins from business accounts in search and category results. Pinterest is framing the move as an "experiment" for now, while promising all promoted pins will be clearly marked and relevant to user tastes. How thoughtful. And so begins the march towards profitability.