What characterizes a "rare book" I am doing a workshop for librarians
to help them identify books in their collections..donated, gifted etc.
that have potential value as collector's items What to look for?...
first editions, special binding etc.

Hi! Thanks for the question.

The following resources came from library sites and show their
criteria for selecting rare books and other documents for their
special collections.

Cornell University Library
http://www.library.cornell.edu/colldev/RMCTransGuidelines.html 

O?Grady Library of St. Martin?s College
http://www.stmartin.edu/library/collectionDev/Library-SpecialCollections.pdf 

George A. Smathers Libraries of the University of Florida
http://www.uflib.ufl.edu/cm/cmdept/Rare%20Books%20Procedures.htm 

Georgia State University Library
http://www.library.gsu.edu/spcoll/rarebooks/developmentpolicy.htm

American Library Association
http://www.ala.org/ala/acrl/acrlstandards/guidelinesselection.htm 

Thomas G. Carpenter Library
http://www.unf.edu/library/sc/rarematerials.html

The University of Texas at Austin Library
http://www.lib.utexas.edu/admin/cird/policies/subjects/specialprotection.html 


This page from the Canadian Library Association shows some ethical
practices in collecting rare books for libraries.

Canadian Library Association
http://www.cla.ca/about/special.htm 


Search terms used:  
library "special collections" criteria rare books

I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
                                                          
                              
Regards,                              
Easterangel-ga                              
Google Answers Researcher

Thanks for the nice links.  I would have loved to have you
summarize/analyze a little, for the five star rating.

Some of the information here may be helpful:

http://fostoriatradingpost.tripod.com/discuss.htm#how