I've had a Kindle 3 since Christmas and really like it. The screen is the best feature for me - the E-ink is much easier on the eyes than a back-lit screen.
When I first got it however, it crashed regularly (two to three times a day). After a few searches on the internet I discovered I was not alone in this and was surprised that it was the Amazon official cover (the one without a built-in light) that was the problem! Common theory is that the (painted metal) clips that hold the Kindle into the cover conduct just enough electricity to cause a brown-out in the CPU. To test whether the cover was the cause of my problems, I removed the cover about a week ago and my Kindle has not crashed since.
I find it incredible that Amazon continues to sell a product that causes such a wide-spread problem. Especially considering that it makes one of their key products, the Kindle, look really bad. I imagine they've had to swap out many Kindles with disgruntled customers whose Kindles have crashed regularly. I am keeping my Kindle, but returning the case and will buy a third-party case that does not clip in. I'm not all that happy about it though as the Amazon cover is really nice, but the regular crashes and potential for long-term damage to the Kindle, are unacceptable.