Amazon (Nasdaq: AMZN) just made its Amazon Prime service a little more, well, prime. The company has launched a digital-book lending library for Kindle and Kindle Fire owners who also subscribe to the program.

The program, which goes by the less-than-imaginative name Kindle Owner's Lending Library, will allow Prime subscribers to borrow one book per month. Unlike e-books you might borrow from your local public library, you can keep the title for as long as you like. However, the book will disappear once you borrow another.

Overall, I'm excited about the program, but I see a couple of potential setbacks. First, because the lending library is clearly a ploy to drive sales of Kindle devices (meaning you can't access the library through the Kindle App), Apple (Nasdaq: AAPL) iPhone and iPad users are out of luck. Also, as much as I love my Kindle, browsing for books on the device is a somewhat miserable experience.

Second, the library is on the small side. Right now the selection is limited to about 5,000 titles. I would expect the library to grow eventually, but at the moment, the six largest publishers haven't signed on, citing concerns over the program damaging sales of older books. However, the library includes best sellers like The Hunger Games by Suzanne Collins and Moneyball by Fool favorite Michael Lewis.

That being said, even if the library isn't an instant success, it should help Amazon in the long run. At its most basic, the promise of free books as well as access to Prime's streaming library could convince undecided consumers to pick a Kindle over Barnes & Noble's (NYSE: BKS) Nook. Additionally Amazon's more complete ecosystem also make the Kindle Fire a more compelling choice than GameStop's (NYSE: GME) gaming tablets.

The other benefit of adding more features to Amazon Prime is that each new bonus makes the service a little stickier, which can help drive Amazon's regular e-tail sales. For example, I'll admit that I'm one of those fools who signed up for Prime to get free shipping on a large order and then forgot to cancel before the end of the trial. I have since acted like I did it on purpose and have bought more from the site than I would have normally.

I had planned on canceling at the end of the year, but I think one free book a month plus free shipping and the occasional streaming video is worth $79 a year. I'll probably keep it and consequently spend more of my shopping dollars on the site. If I weren't so pleased with the service, I would be tempted to call Prime a stroke of evil genius. Well played, Amazon, well played.

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