I "upgraded" from a K3K to a PW today, and so far I'd say I'm on the fence. The screen does not have as much contrast when the light is "off" (set to zero, which is still ever-so-slightly on) which is a big disappointment to me. To get the screen to look better than the old K3K screen, I have to turn the light up to about 12 (a little less than half) - at least that's how it looks indoors to me. That said, I'm enjoying the touchscreen more than I thought I would. Navigation is still a little clunky in periodicals, but in books it's great and being able to highlight and share through the touch interface is much better than using the d-pad, as is navigating the store with the touchscreen + virtual keyboard. Collections are also pretty easy to manage, I find, but that's not something I use much.
There are a few things I would change on the KPW (like being able to turn off the light for real!) but so far it's pretty good. I'm going to live with it for a week and see how I feel. It might stick, but I might just keep the K3K until the KPW2 comes out and imrpoves things like contrast and lighting.