The Nation Bureau of Economic Research (NBER) said that the US has been in recession since December 2007. Of course, that is precisely the time I had given here on The Futurist, except that my declaration was back in February 2008. So I arrived at the same timing estimation, just 10 months before the Federal Government, back when knowing this would actually have been useful.
The longest post-war recession in the US lasted 16 months, so if this recession lasts beyond April of 2009 (which it very well may), it would be the longest post-war recession the US has had. Of course, this recession was shallow for the first 10 months, and only turned sharply lower in October of 2008, so 'duration' is not the whole story.
At present, the consensus is that all of 2009 will effectively be recessionary, putting the recession at 24 months in total duration. Whether this occurs or that pessimism itself is over-shooting remains to be seen.