Many libraries now have e-books available (here's SPL's digital library), but the system still doesn't feel very modern; for the most part, libraries can only loan out one copy of the e-book at a time. I can understand why that is the way it is, but it's preposterous to loan a digital copy out the same way you loan out a physical book.
The Wall Street Journal reports that some libraries have joined together to launch Open Library, a new way for libraries to deal with e-books:
Starting Tuesday, a group of libraries led by the Internet Archive, a nonprofit digital library, are joining forces to create a one-stop website for checking out e-books, including access to more than a million scanned public domain books and a catalog of thousands of contemporary e-book titles available at many public libraries.
It's fairly equivalent to Google Books, but it's more open-source. As a real first step toward the digital future of libraries, it's very interesting.