This is a US only version (compared to the Global Wireless version) and gets worse battery life. Non-issue if you don't need the additional battery life and you don't need 3G outside the US.
Again, on 3G... Just downloading books, really NBD... This is not a replacement for a laptop or anything.
But the battery life is definitely one to consider. The newer model (which you'll spend almost double on... $190) gets about double.
But the battery life on the Kindle is still rated in days and weeks, not hours... No matter what model you get.
I agree, they're for two different purposes. I see no need for 3G but others do... and I tried my PDF's on a friend's DX and they were no better than on the Nook. I might have to end up converting them to ePUB and hopefully being able to edit them to work better.
I think these still have wifi, so worst case scenario is that you'll have to stop at a mcdonalds or starbucks while on the road.