@jhowell - great idea!
I just installed your plugin, and added spl.lib.overdrive.com, and made it the first library in the list.
I then added an empty book in calibre, then populated it with 'A Short History of Nearly Everything' by Bill Bryson, then searched for the book.
Running in debug mode, I see that your plugin found the book with 100% confidence.
However, it then crashed with the following traceback:
Traceback (most recent call last):
File "calibre_plugins.overdrive_link.dialogs", line 79, in do_book
AttributeError: 'ApplyProgressDialog' object has no attribute 'ids'