Amazon has announced a software development kit for the Kindle. This is clearly an attempt to shore themselves up against the tidal wave of interest that Apple's forthcoming tablet computer is going to generate.
The Kindle is an excellent piece of hardware with absolutely dynamite battery life. It's definitely an adjunct to a "main computer" (or even a main laptop), but I would love to have, for instance, a Kindle-based blog reader.
I've had several ideas for Kindle apps and look forward to receiving the SDK. The Kindle's internal software is programmed in Java, so I expect the SDK to be Java-based.
On the other hand, I fully expect to swoon at the Apple Tablet. I spent years developing Tablet PC software for Windows and was tremendously frustrated by the lack of uptake. The Tablet form-factor has lots of challenges, but with the iPod and iPhone Apple has proved their ability to "think differently" and create winning hardware/software solutions.