in regards to the flex of the wings, this is an evolution in wing design from the delta wing design. Similar to the winglets for example on 737NG's (and perhaps the A380 and others) in regards to reducing lift induced drag caused by wingtip vortices.
The flex wing design also has raked wing tip technology! (only just noticed it on Scott L's photos) which both complement performance enhancing efficiency, and safety to a degree. Flex wing, blended winglets & raked wingtip technology tend to be advantageous at higher altitudes.... blah blah,
Viva La Evolution, Viva La Boeing.
And what about the interior, liquid crystal windows, overhead space, just beautiful.
http://www.newairplane.com/787/virtualTour/