That "drop" is a result of several things not the least of which is the millions of people who have stopped looking for work have been subtracted from the "civilian work force".
By reducing the size of the "work force" the BLS can manipulate the "unemployment rate" to either keep it the same or show a slight improvement even though other government reports show we are losing jobs 12 times faster than we a "creating" jobs.
Remember the 120, 000 reported new hires for the whole month of April? Well, for the same month over 1,400,000 people filed for unemployment for the first time.
A new report for the week ending March 14 was released today. There were 386,000 initial unemployment claims for the week.
http://www.dol.gov/opa/media/press/eta/ui/current.htm
If you want to see the weekly reports since January 2010 go to this link:
http://www.ows.doleta.gov/unemploy/claims.asp
Be warned! It's an ugly sight.