Dominic Gates put out an extensive article detailing Boeing's struggles with making sure that the passengers on a 787 can survive a serious crash of the aircraft. Boeing engineers were raising red flags as early as 2005 about some serious issues including the survivability in crash. The survivability results for the 787 were compared to that of the 777 and in early simulations showed that the 777 was more survivable.
Boeing has since made changes to make the 787 more survivable in an impact. You can read more in Dominic's article:
Dominic Gates : How will 787's new materials fare in a crash landing?