The Boeing Dreamliner was launched for the first test flight yesterday.
The Boeing 787 is around the same size as 767-300. However the 787 is planned to be 20% more fuel-efficient than the 767. The efficiency comes equally from improvements in the engines, aerodynamics and reduced weight by use of composite materials, and the use of improved systems.
20% improvement in efficiency should translate into a 15% saving in operational efficiency.
Each plane can interchangeably use either the General Electric GEnx or Rolls-Royce Trent 1000, due to the design of a common interface. The Rolls-Royce engine was used for the test-flight.