According to the National Bureau of Economic Research the the longest post war economic slump has ended after 18 months.

The Business Cycle Dating Committee met and determined that the recession ended in June 2009, after having began in December 2007.  That means any further economic slow down will be considered a new recession even though the effects from the last one can last much longer. 

I doubt that the people still out of work will find much solace in technicalities, but growth is growth. 

Read the report here.