Amazon has finally announced its long-anticipated Kindle lending library, allowing Kindle and Kindle app users to borrow Amazon's e-books from thousands of libraries across the US. Users will be able to find the Kindle books on their participating public library's website and check them out through Amazon, which will send the book directly to users' devices over Whispersync.

"Libraries are a critical part of our communities and we're excited to be making Kindle books available at more than 11,000 local libraries around the country," Amazon's Kindle director Jay Marine said in a statement. "We're even doing a little extra here—normally, making margin notes in library books is a big no-no. But we're fixing this by extending our Whispersync technology to library books, so your notes, highlights and bookmarks are always backed up and available the next time you check out the book or if you decide to buy the book."

The ability to make notes and highlights—and subsequently sync them back to the system for review later—is certainly a major plus. The downside, of course, is that the e-books have to be "returned" after a certain period of time, just like any other library book. Amazon doesn't specify on its site how long the books are borrow-able for, but when asked, Amazon spokesperson Kinley Campbell said that the expiration time varies by library and by the book.

"Generally [it will be] 7-14 days," Campbell told Ars. "We recommend checking with local libraries on questions related to availability and specific books."

Seven to 14 days isn't a lot of time to read an entire book for some people, but it's hard to argue with free, borrowed books. Our only complaint with this announcement is that there seems to be no comprehensive list of the 11,000 participating libraries—even Amazon's FAQ page about public library books remains vague on this question. The requirement is that the library offers e-books via third party service OverDrive, though, so it's safe to assume that most major libraries will be participating to some degree or another. (You Chicagoans out there get to be lazy, as I've already confirmed that Kindle books can be found via the CPL website).

Edit: Removed links to Amazon due to technical (CMS) problems on our end. See comments for proper links for now.