In terms of weight the 787 is not a lightweight in spite of its carbon fibre construction.When I retired my employer had recently introduced the 788 GE powered replacing the 763 with very similar pax capacities.In terms of Zero Fuel Weight a fully laden 763 weighed the same as an unladen 788 rather breaking the myth of lightweight construction.I am guessing the use of materials was quite conservative and that the weight of the generators and new style compressors for the pressurisation has pushed the weight up.The 787 fuel burn in the cruise is very low provided the sector length is long.It is not nearly as improved on shorter sectors.I am led to believe my former employer continues to despatch an engineer on the flight deck when operating to short haul destinations without engineering support such is the types voracious need of maintenance attention.Doubt has been raised over whether Boeing have made any profit from any of their 787 sales given the complexity of construction and the cost of modern materials in the aircraft.Boeing has certainly made efforts to reduce the amount of titanium in the airframe some components of which had a 98% wastage rate in manufacture.My colleagues flying the 787 loved it when it was working but it had a very challenging entry into service and continues with the temperament of a thoroughbred racehorse.One of aviations classics...I suspect not ...more an interim pathfinder.
Regards Stampe