Thanks to everyone who commented on my question regarding proxying  
Google Book Search.

On looking into this further, it appears to me that current techniques  
for proxying would not be able to enhance privacy for Google Book  
Search once the provisions of the settlement agreement are  
implemented. http://go-to-hellman.blogspot.com/2009/08/what-google-books-settlement-agreement.html

I am in the process of looking at other technologies to see if there  
are alternatives. Hence another question: Does anyone know of  
libraries that have done anything with "attribute release" in the  
context of SAML/Shibboleth?

Thanks!

Eric Hellman
President, Gluejar, Inc.
41 Watchung Plaza, #132
Montclair, NJ 07042
USA

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http://go-to-hellman.blogspot.com/