PC World: Next time you start a conversation on Facebook about that new shirt or watch you bought, you might be unwittingly delivering juicy feedback to the retailer. Facebook plans to start funneling more of its data on users’ activity to marketers, to give them a better sense of what people think about their products, and better identify the types of people who are talking about their products. This pipeline of data, which Facebook calls “topic data,” is being developed in partnership with DataSift, a data analysis company.