Another reply in this thread cites some of the research on IQ score trends over time. There probably is more gain yet to be had among disadvantaged populations than among advantaged populations (which have already enjoyed huge gains), but the mechanism of causation of IQ gains is unclear enough that there may yet be a lot of room for increase for all populations.
Even if IQ gains grind to a halt in particular places, there is still much to be done to raise the level of rationality in the population there. (Another reply to this thread just cited Keith Stanovich's recent book What Intelligence Tests Miss,
which is all about how to improve rationality among people of various IQ levels.) And for general social improvement, it is also possible to shape public policies so that they take into account common forms of human irrationality,
Even if IQ gains grind to a halt in particular places, there is still much to be done to raise the level of rationality in the population there. (Another reply to this thread just cited Keith Stanovich's recent book What Intelligence Tests Miss,
http://yalepress.yale.edu/yupbooks/book.asp?isbn=97803001238...
which is all about how to improve rationality among people of various IQ levels.) And for general social improvement, it is also possible to shape public policies so that they take into account common forms of human irrationality,
http://www.amazon.com/Nudge-Improving-Decisions-Health-Happi...
so that daily life is more sound even if the people living it are neither more intelligent nor more rational.