Th trend line has been toward significantly less mobility relative to past decades--though you'd probably want to correct the numbers for demographics given that 20 somethings move the most (as one would expect).

Exactly-- the number of young people still living at home has surged in the last decade. This is not surprising given that "starter homes" are one of the main targets of housing speculators. People who would buy their first house rent longer, driving up rental rates and putting the transition from family to independence further out of reach for many.