I love to see that I have a resource referenced in a footnote. I also like to know which one's I do not have in my library. I would love to see a library Lookup tool, like the power lookup tool, that shows the resources I have and the one's I don't have as I read through a resource. It could function as the reading list does, with a locked/unlocked indicator beside each resource.
Hovering over the resource would show the description of the resource, regardless of whether I own it or not (yeah, I know..I'm dreaming) so the reader can determine the validity/scholastic level of the reference.
I could even see this increasing sales as people say "I really need to see what that resource has" :-)