My experience with my Kindle is that these tablet-like devices can be slippery, even in a case. You tend to carry them around in your hand, nestled in with your papers or books,, while juggling a drink in the other. I've fumbled and then drop-kicked my Kindle several times, as often open while reading as when transporting it from room to room.
It seems counter-intuitive, but the hard leather case on my Kindle is the goldvstandard in cases for me. The stiff, wrap around leather case
1. absorbs drop shock at the corner beautifully & it protects well.
2. It can be bent double, like breaking the spine of a book, so that you can grasp both the case AND the device in one hand
3. It has a positive mechanical lock on the edge of the device to ensure the cover never comes off in a drop.
So far I haven't found a great iPad case that both offers a high degree of protection to the device but is unobtrusive to use. The forthcoming Otterbox look quite protective but also clumsy to use.