I found these numbers from Disruptive Library Technology Jester from the supporting documents for the Google Book Search legal settlement interesting:
“Dan Clancy is engineering director of the Google Book Search project, so he has a unique insight into the inner workings. Grimmlemann notes that Clancy states:
■ To date, Google has Digitized over twelve million books, and intends to continue Digitizing books in the future.
■ Google has received metadata from 48 libraries.
■ Google pays approximately $2.5 million per year to license metadata from 21 commercial databases of information about books.
■ Google has gathered 3.27 billion records about Books, and analyzed them to identify more than 174 million unique works.”
■ “Google has developed algorithms to compare these numerous sources of metadata and identify the most accurate data about each book.”
I’ll bet a lot, if not the majority, of that metadata has a librarian’s fingerprints on it.