I'm still loving my Kindle 3. But I admit I'm intrigued by the PW. When I consider upgrading, a couple of things stand out for me.
I don't want to give up storage on a non-expandable device. Period. Why do I want all my books loaded? So I can do the periodic search for the quote or phrase that I'm sure I read before without going back to my computer. (Was that Shakespeare, or Harry Potter?") I also have an inherent mistrust of "The Cloud" - reminds me of all the horror movies with the same naming structure like "The Blob" or "The Thing"...
The thing that would really tempt me to upgrade is higher resolution eInk. After seeing the difference resolutions makes in LCD screens, (Fire vs Fire HD) I can't wait to see what "HD" eInk looks like.