I don't like apps on my Kindle but I like the Kindle app on my phone and iPad. I use my Kindle device for book reading only. The Kindle app is impressive for viewing illustrated children's stories and cookbooks on the iPad. The app also comes in handy for reading in the dark.
One noble feature is that you don't need to own a Kindle device to use the Kindle app. You'll have to order your books from Amazon.com from a computer web browser or through Safari on your device. After that, your book will upload in seconds via wi-fi.
As of yesterday, Kindle and Kindle app users can borrow books from their local libraries. You will need a valid library card and your library will need to offer the digital service OverDrive. According to Amazon, "Kindle books are now available at over 11,000 local libraries."
Since my local library is pretty much off the map unless a hurricane is coming, I doubt I'll get to take advantage of this service anytime soon.
Lastly, if you get stuck somewhere without your Kindle device, you always have the option to read your book from your phone.
Click here for more information on borrowing Kindle books from your local library.