Key_Master - 2:26 am on Feb 22, 2011 (gmt 0)
I can't speak for Nook but I do know that you can only lend ebooks from one Kindle account to another if the publisher allows it and then only for 14 days. If the publisher does allow it, the person who lent the ebook will not be able to read their copy until the ebook is "returned".
In regards to the sharing feature Amazon now offers to Kindle users- you can only share ebooks with up to six devices registered to your personal Amazon.com account.
Libraries generally only have one or maybe a handful of certain titles on hand at one time. These are lent out on a first come, first serve basis and you are required to return it within a specified time period. They aren't mass producing copies and handing them out to the general public for free.