John Blyberg (creator of AADL.org and now at Darien Library) posts about the new version of SOPAC-- a "Social Opac" discovery layer which, it seems, will be ILS-independent. SOPAC 1.0 works with III (or "Millennium") ILSs and Drupal, and apart from normal catalog searching, it adds features like tag clouds, reviews and more.
It seems to me that if SOPAC can have an abstraction layer so that you can plug in translators for different ILSs, it really opens the door to using all of the great modules we already have in Drupal and have the tools to "easily" build Library Catalogs Just The Way We Like.
This is our philosophy--and I guess John's--for picking Drupal: have a solid base (in code AND community) from which to build on, and... build!
I envy Darien Library, I'm sure they'll get a great new website to match their library =) Full steam ahead!