I swapped my K3 with keyboard for a K4. My pal at work was happy to get my K3 WiFi and cover for $60. The K4 is *much* smaller and lighter and seems to respond more quickly. The screen is even a little clearer but not by much. For long reads the light weight is a *huge* win.
On Friday I also ordered a Kindle Touch SO WiFi and expect that to be Nirvana.
I tend to bookmark a lot as I read because I found that the page turn buttons on the K3K are easy to bump and the bumps occur enough to be annoying.
The K4 has no dedicated Bookmark button like Alt-B so it takes "menu | down x 4 | Select" to make a bookmark. The Kindle touch should solve that issue completely one way or the other.
Finally there is no audio on the K4 and I wish there was a way to order a Kindle Touch without it as well. I understand why Amazon made the choices that they made given that they own Audible, the audiobook service, but honestly feel that Audiobooks are better on the iPhone 4.
As an iPad owner I have absolutely no need for a Kindle Fire. IMHO only inexperienced eBook Readers (the human kind) use a heavier LCD device as a reader. The light kills your eyes after a few minutes. The Kindle Fire will do well as a multipurpose device but there really is no need for a single device to do everything so I will not buy one.
So there you have it. I'm a typical Kindle customer with my own set of preferences who is looking forward to November.