Steve Horwitz has an interesting post on income mobility, showing that lots of people move up from the lowest quintile of earners over time -- over half during the nine-year period studied.
But I wonder how high a percentage of the people moving up had parents in upper quintiles already? All around me in Brooklyn I see people in their 20s and early 30s, from middle or upper class backgrounds, spending a decade or so bartending, waitering, trying acting or music or writing -- spending all this time in the bottom quintile -- then getting married or giving up on painting and "getting a real job," and rapidly rising into the quintile their parents raised them in. These are all just delayed "adulthoods" (the quotes are because I'm not accepting the idea that giving up poetry and going to work for Goldman necessarily represents "adulthood") and not real income mobility at all, or at least not what I would take to be the crucial aspect of income mobility, which is class mobility. (I.e., the phenomenon I just described has nothing to do with whether or not ghetto or rural poor families are moving up the class scale over time.)
It would be very interesting to find out just who is doing the moving.