just spied on fm: Bookbase [1] is a gui front end to a mysql database of books. Records are keyed by ISBN. Could be useful for personal collections... would be nice to hook up to a cuecat reader with a z39.50 client [2]. :) Hint: it won't build unless you have the mysql-shared libmysqlclient stuff installed.
Links:
[1] http://bookbase.sourceforge.net/
[2] http://www.sujal.net/tech/cuecatisbn.perl