One big issue raised by people skeptical of Boeing's extensive use of composites for the fuselage of the 787 is the aircraft's ability to survive lightning strikes. Scott Fancher revealed to Bloomberg that ZA001 was struck by lightning during a test flight over Puget Sound. The strike was inadvertent but the aircraft and its systems survived the strike with no issues found after the aircraft had landed. Boeing has invested much to make sure that the all electric jet is well protected from lightning.
Additionally, Fancher revealed that Boeing flight test pilots have completed 40% of certification test points over the 1000 plus test flight hours that the test fleet has flown. Given this progress it may take Boeing much less than the stated 3,100 hours of flight test to complete the flight test program. Fancher says that test flight results are matching up to model predictions quite accurately thus adding to confidence in the program. If this trend continues I think that there will be a spike in 787 orders in the coming months as Boeing and it's customers get comfortable with the results coming out of the test flight program.
Bloomberg: Boeing 787 Withstands First Lightning Strike as Tests Advance