As of 2004, 9.9% of US employed were in construction and real estate. Was 9.3% in 2000. Maybe it is >10% by now.
http://www.census.gov/prod/2005pubs/06statab/labor.pdf
I realize this includes commercial, not just residential. My impression is, commercial RE is stll doing well, not in a bubble (but I don't have any info - anyone know?).
But still, seems like employment is going to get pretty tough for say 5-7% of the US population. Might move unemployment from current 4% to - what, 5-6%?