I've heard the story where there was a 10x difference in the time it took CS students to complete a series of system programming assignments, but are there other anecdotes out there?  I'm very suspicious of this story, and think that a lot of this fabled 10x multiple can be explained by extrinsic circumstances or luck.  At least that's what I've observed in science where easy experiments in a field that is new and fashionable can yield lots of interesting papers, where taking on more difficult projects in established fields can require much more work to achieve incremental results.