The 2010 edition of the General Aviation Manufacturers Association Statistical Databook & Industry Outlook http://www.gama.aero/files/GAMA_DATABOOK_2011_web.pdf [2] was recently made available through the association's website. It is a great source of statistical information for US and international general aviation, as well as, a resource for trying to figure out the future of the industry.
Links:
[1] http://www.library.northwestern.edu/libraries-collections/evanston-campus/transportation-library
[2] http://www.gama.aero/files/GAMA_DATABOOK_2011_web.pdf
[3] http://www.library.northwestern.edu/related-pages/general-aviation