Not long ago some spoke about tearing down some of the newly built homes in Stockton and Modesto because it could not sell... there are cities in the rust belt which saw prices drop pretty deeply. It is very believable to hear that home prices are half or more today. No one would believe that in 2003.
A lot of places have gone down like 70%. Of course, those are bad neighborhoods or overbuilt areas. My prediction is: if there is another financial disaster in 5 years, another step down. So, 70% off the peak is definitely possible. If no, then we will hover around current level or somewhat lower.