You asked about libraries in non-SL virtual worlds. My short answer is that I don't really know of any, and I've kept my ears out for them.
I spent several months preparing to start a library in Caledonia on BlueMars. So far as I know, this would have been the first library there. I abandoned this when they converted to being an iphone app. My understanding is that now they are primarily for people who use avatars as virtual paper dolls.
There is a librarian's guild on WoW, but I don't think they actually operate any libraries.
I'm currently involved in planning a library for the 911 First Responders Memorial site on Virtual Worlds Grid. I've been given a site, but so far the library exists only in my brain.
I'm very curious whether any of the educaitonal projects that have moved to Reaction Grid or other OpenSim grids have associated libraries.
I'm a teacher librarian & recently started a community based blog for getting boys to read - http://GettingBoysToRead.com. Please send me a friend request if you'd like to network, share ideas, and learn more about getting boys to read.