I would not be without mine. The books on mine are mostly freebies by Twain, Jules Verne, etc. They cost $0. Also have a bunch that were in the $.99 category, with the most I have paid being around $10 for a newly released Vonnegut.
You do not lose books if you have a problem. Everything is online at Amazon, and even if you screw up and accidentally delete one, it is free to re-download it. Don't ask me how I know this.
Can also back up on your pc. By the way, you can also read all the same stuff you have bought on Kindle for PC, or Kindle for Blackberry. So, you can buy the book, then read it on any of several options. It will even keep you at the latest page you have read, no matter which of the options you use to read. Not limited to just the Kindle.
Biggest advantage for a voracious reader like me, is that I can take an entire library of my favorite books, new stuff to read, magazines like Reader's Digest, newspapers and so on, everywhere I go in a device the size of a book. Coolest thing ever developed for a reader, and the Kindle is the best of the breed, I did extensive homework before buying, and I'd buy another one today.