Ross Douthat has some info on a new study. From the paper’s findings:

A large literature has documented a significant increase in the return to college over the past 30 years. This increase is typically measured using nominal wages. I show that from 1980 to 2000, college graduates have increasingly concentrated in metropolitan areas that are characterized by a high cost of housing. This implies that college graduates are increasingly exposed to a high cost of living and that the relative increase in their real wage may be smaller than the relative increase in their nominal wage. To measure the college premium in real terms, I deflate nominal wages using a new CPI that allows for changes in the cost of housing to vary across metropolitan areas and education groups. I find that half of the documented increase in the return to college between 1980 and 2000 disappears when I use real wages. This finding does not appear to be driven by differences in housing quality and is robust to a number of alternative specifications.

Emphasis mine. In other words, relative to people without college degrees, you make more money with a diploma than you used to — but in order to find a job in your field, you have to move to a big city and blow half that extra money on rent.