It’s not a huge overhaul — as in there are very few new features — but Google Books’ Library feature (goes to my library) has just gotten a (weak) social layer. You can now add a user to your “Favorites” (separate from all of Google’s other bookmarking or link-saving or friend-type applications), but it doesn’t really do anything at the moment except pop up a section on your own library page with links to your favorites’ libraries. Hopefully there will be more involved in the feature later this year as Google continues making enhancements.
The controls for dealing with items in your library have also been streamlined to the point of no longer having to leave the library page to change a book’s labels or ratings, or to attach a note (which if I’m not mistaken is another new feature) to it. I’m glad to see these enhancements (which are partially covered on Inside Google Book Search), since always changing pages was really frustrating usability-wise. Good work, Google! Keep the enhancements coming!