It looks like a large number of bitcoins is waiting in very old accounts untouched for many years. Approximately 30% of bitcoins have not been touched for more than 2 years. So a total of 15% of all bitcoins to by mined are still in the hands of developers and early adopters. This is not much, given the value they created for the global financial system :-)
Obviously this includes coins which are to be considered lost forever.