The application of SOA and Web services to library systems is an area that DLT is starting to explore. Maintaing our current ILS takes a lot of our cycles but we realize that we need to put our heads up and position ourselves to support the next-generation ILS. Our colleagues in ITS are looking at SOA too, and we're collectively "organizing to be organized" around SOA - taking an enterprise and architectural approach so we can best leverage the benefits of SOA and avoid standards-collisions.
Here's a link to a useful three part article by Peter Murray (aka the Disruptive Library Technology Jester) that first defines SOA, then shows how it would work with WorldCat as an example, and finally how it would enable the "dis-integration" of the hitherto monolithic ILS.