There are a lot of books that people recommend to me that sound awesome but I don't quite want to own or read right away.
Imagine if you could select an ISBN number, or just visit the amazon.com page for a book, and click on a button in your browser. The plugin would automatically add it to your list of holds at the Seattle Public Library. You'd have to store your library number and PIN, and preferred pickup location with the plugin.
But after that, SPL will just send a notification when the book is available. Takes the hassle out of borrowing.
Also cool would be a wishlist importer that takes books (and maybe even cds and dvds) off your amazon wishlists and adds them to your list of library holds...
If such a thing exists, or if you write one as a result of this post, please let me know as I'd like to use it :)