Can someone venture some guesses as to what types of apps will be created? That screen seems like a terribly limiting factor for apps...
I would guess amazon would only allow non-networked apps
Remember, the 3G modem really was only used in the first place so you can seamlessly buy books from anywhere, on the go. Anywhere there is WiFi, there is almost always 3G/1Rtt, and WiFi is more complicated for the uneducated consumer than an on-off connection as simple as cell phones. All the user even needs to know with cell phones is "I have reception" or "I don't", instead of signal strengths of different networks, what key & kind of key to use, what networks are not safe, and so on.
Let's not forget one of the common reasons for hybrid 3G/WiFi usage is to avoid billing on the cellular network. Notice, that problem is gone for the end user with the Kindle.
Seriously though, let's consider. I hear of tons of apps that are really clever on the iPhone store, and many of them do not use the camera, gfx, gps or accelerometer. It's true the iPhone has more computing power, but both have 3G.
My mind's not in a state right now to do a real comparison, but in my opinion, quite a number of the clever and/or useful iPhone apps I've seen could be ported to the Kindle. (this is not of course to say that's what should be done, or even that would be the limit- after all, Kindle has a much larger screen- just as an idea of the spread!)
Interactive books are an obvious thought. Interactive maps might also be useful.