I was curious, and looked it up on the Bureau of Labor and Statistics website. If I'm reading that right, Civilian Labor Force, Employed, Percent of Population peaked in 2000 at 64.4%, which is 5% higher than 2000 levels.
Looking at the wikipedia definitions (especially that third image), I think the interesting metric is the employment-to-population ratio (i.e. all employed people over all people, eligible to work or not). That default view does show a 5% drop since about mid-2008 that never recovered. It was previously around 60% in the early eighties (if you adjust the graph to start from the earliest available year, 1948).
Also interesting is part time workers as a percentage of all workers, which was a sharp (3%) increase in 2009 and slowly dropping off at 0.2% per year (eyeballing it).
Other interesting stuff can be found in this PDF of charts. For example, on page 17 it shows that most of the layoffs in 2008/2009 were permanent, not temporary.
Thanks for leading me to look at this stuff; it's rather interesting.