With American Airlines just starting to fly Boeing 787 Dreamliners in passenger service. it comes as a surprise that one of them is being dedicated to cargo service. Boeing is still considering when (or if) to create a 787 freight version as it has successfully for the 767.
American's 787 cargo routes started June 2nd with DFW/Beijing and June 4th with DFW/Buenos Aires, and will add DFW/Shanghai June 26 and Chicago/Tokyo on August 18th.
In those four markets, the 787s larger cargo capacity (28 positions vs 20 for the 767) and improved fuel economy and power, make a difference for shipments of high-value or perishable cargo, accoring to AA Cargo. The plane can carry up to 1000 pounds of dry ice, critical to perishables.
In the long run, AA Cargo expects the 787 to replace most of its 767 freighters.