I have just completed a short piece on the impact of regional prices on the measurement and geographic distribution of low income individuals. Basically, Youcef Msaid and myself* used the March 2012-CPS data combined the BEA's regional purchasing power parities database to correct incomes.
We found is that the level of inequality is very modestly overestimated (0.5%). Now this is a conservative estimate since we used state-level corrections for price differences. This means that we took price corrections for New York state as a whole even if there are wide differences within New York state. Obviously, with more fine-grained price-level adjustments we would find a bigger correction but it is hard to imagine that it could surpass 1-3%.