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From 2006, sponsored by National Geographic (it's a PDF file):
http://www.nationalgeographic.com/roper2006/pdf/FINALReport2006GeogLitsurvey.pdf
I take back what I said about Alaska and Hawaii, at least based on this survey. The overall score had 94% of people being able to find the US on a map, but the map that they have in this survey only shows the continental US as a potential answer (from what I can see.)
I think it was the one from 1998 that had the AK/HI conundrum, I'll see if I can find that one.