Credit:
The Kindle OS is Linux with a special set of drivers; we're sure that someone, somewhere will thoroughly comb through it and reveal more details, particularly about its DRMed parts.
In practice, this means (if the code is released under GNU GPL, as Engadget suggests) that manufacturers can now build a Kindle clone. While Kindle is a solid device, it's definitely not perfect, and we're definitely interested to see what the competition will do with the code.
The source code is available here.