Just thought I'd point this out. I spotted that the GET List subscriber method was just returning user information of the individual who created the list. As it turns out I was doing a POST, not a GET as specified in the docs.
As soon as I changed it to a GET I got back what I was expecting. A few other of the list methods that are documented as GET to seem to function with a POST. http://apiwiki.twitter.com/Twitter-REST-API-Method:-GET-list-subscribers Cheers, Rhys