Without getting into circulation statistics, you can quickly determine the popularity of subject areas by using the Saltometer.  Here's more info on the Saltometer.  What does your library's Saltometer have to say about your collection?

I have heard that a public library just over the border in Massachusetts, is switching from the Dewey system to the BISAC system, which is currently used in book stores.  If you, like me, are not familiar with the BISAC system, check out the October 1, 2009 edition of Library Journal.  The cover story is titled, "The Dewey Dilemma" by Barbara Fister.  Has any NH library made the switch, or is considering it?  Thoughts?