Like many others (saw at least half a dozen), I carried a Kindle on the trail this year.
The device held up well with no problems over the 6 weeks/500 miles of trail which I traveled. Battery life is exceptional, but maybe not the "up to 30 days" claimed. Even so, it never ran out of power on the trail and I only recharged it once. (make sure the wireless is turned off)
I noticed that at cool temps of say 40 degrees or less, the screen takes a second or two to update - significantly longer then at warmer temps. This makes flipping pages a little annoying. Using the Kindle at even colder temps during the winter or late fall may not be practical.
All in all, I feel it was well worth having the Kindle along and it got used everyday - especially since I had the Companion trail guide loaded into it and did not carry a hard copy. The only problem with that was I was reluctant to take it out of the pack if it was raining.
I only wish the Kindle had the ability to write and up load trip journals. Will have to suggest that to Amazon and maybe they will come up with something - if enough other people ask for that feature too.