The Kindle is an amazing gizmo. The Kindle 2 can hold over 1500 books. This is an amazing small library. The only problem is that it IS an electronic gizmo. Like any piece of electronics you can break in scratch from rough usage. You can toss a normal book across the room with no ill effect, I would recommend that for Kindle.
This does not mean the Kindle is inherently fragile and extremely breakable like a delicate piece of China. Kindles are designed to be sturdy and stand some punishment. To make things even better there are covers and cases they can be bought for the Kindle that make them even more resistant to casual usage.
Sleeves, Covers and Cases are the primary methods of protecting the Kindle. A sleeve is basically just a holder that the Kindle to be placed inside of for transport that will protect it from scratches and some crushing damage. Think of it as a small bag for transport. The case on the other hand is also primarily used for transport but has a far more rigid design. The case will also protect against random scratches but is also designed for much better crushing protection. A cover will stay on the Kindle at all times and you have a very some hours of protection. The Kindle will snap, slide or tie into the Kindle based on the design and this cover will protect the Kindle at all times, like the cover of a book.
Sleeves are generally the least expensive. They can go from simple yet fashionable cases made of neoprene like the Laurex which sell for $12.99 up to fashionable quilted nylon cases that sell for up to $35-40.
The Kindle case is far more rigid and offers far better transportation protection. These cases come in everything from hard plastic to both fake and real leather. The price varying along with the look, quality and strength of the item used to encase the Kindle . Thule makes a specific Kindle case for $39.99 that looks like your Kindle could survive a direct nuclear blast and remain undamaged.
The final type of Kindle cover are the ones that ARE just a cover. They work like a cover on the book where the Kindle slides inside and can be used while using the Kindle as well transporting it. TrendyDigital has a folio case cover of this sort that retails for $25.
Regardless what type of protection you have your Kindle, it is a good idea to have some sort of protection. While Kindle is not fragile it is not meant to be dropped and thrown about in a little bit of extra protection can only help them keep your screen from cracking or scratching.