I think the meager positive inmigration looks much more impressive against the largely negative trend of the last 15 years. Migration tends to slow down during a recession and that effect appears to benefit Pittsburgh. This bolsters the less-people-are-leaving theory. However, as the economy picks up steam (still holding my breath about Europe) I expect the move to Pittsburgh to increase.
Exodus Pittsburgh will pick up, as well. The balance should remain positive. The tell will be 2011-12. (Assuming the EU doesn't melt into a full blown depression) That will be 7-years out from the last net outmigration peak. At that point, I'll be ready to claim that Pittsburgh migration is no longer countercyclical.