How many digital books are there online?

The thought occurred to me to try and determine how many digitized books are now (as of February, 2010) online. Then, I would try to
estimate/guess how many of those are genealogy related.

I realize that the task is likely impossible, but I would like to have some idea of the magnitude of the online book community. My first stop
is Google Books. It appears that Google doesn't publicize the actual number of books scanned. But an article in the Official Google Blog
of October 9, 2009 gave the total at more than 10,000,000. Doing a
quick search in Google Books on the subject of "genealogy" returns
about 26,000 books, while a search on "family history" returns about
17,900. Google Books has three levels of online availability; Limited
Preview, Snippet View and Full View. Only Full View gives the entire
book's contents.

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