This graph is based on the Case-Shiller Composite 20 cities using seasonally adjusted data starting in January 2001.
Most cities were seeing month-over-month increases every month through 2005. In 2006, some cities started seeing year-over-year declines (red). There were still a few cities with increasing prices in early 2007. The increases in 2009 and 2010 were related to the housing tax credit (all of those gains and more are gone).
Recently prices have started increasing in more and more cities. Note: Case-Shiller data is through April.
In April 2012, 17 cities saw month-over-month price increases (SA), and 10 cities saw year-over-year price increases.
I expect that the number of cities with a year-over-year price increase will continue to climb, and in a few months the Case-Shiller Composite 20 index will turn positive on a year-over-year basis.
Click the chart to enlarge