Couldn't resist your suggested search... some interesting reading there. But when I was last active in some of the US expat groups, the estimate of US citizens abroad was more like 4 to 6 million. (As far as I know, the figure is based on compilation of US Embassy and Consulate estimations.)

I do wish they would actually do some research to see how much tax they get or could potentially get from overseas residents, given the various exclusions and tax credits available to most of us. I suspect there are only a handful of US expats who fit the "swilling champagne and caviar" stereotype the US government seems to have of us.
Cheers,
Bev