Got my Sony reader for Christmas and have added a number of books, newspapers and magazines to it. Some from the Sony Reader Store, some from the Gutenberg Project, and some books from my public library.
I have read about 6 books so far and enjoy this book method.
I borrowed Dick Van Dyke‘s memoir from the Midland Public Library and their ebook cooperative, http://www.simcoe.pulse.ca and finished it in two days. The book was borrowed for 14 days, the default loan period. That was when the trouble started. I dropped by at the library on the way home and spoke with one of the librarians who was knowledgeable about ebooks and readers but we could not work out how to return a book early. I puzzled it out last night.
It may be in the user guide but I did not check there. As an old tech writer, that was quite a sin.
With the Sony Reader running and a wi-fi connection, open the Books folder from the Home screen. Change the view of books from cover icons to the text list of books. Then press the options button and go to the second page of options for that screen and view. Return library books is an option that you can select. Only the library books show a check box for you to check to make your selecction of returns. Press done, found at the top right of the screen. And back they go.