Developers at KLab have built an NES emulator for the Kindle. It's more awful than you could possibly imagine.
Beyond obvious display limitations (black and white only), control problems (QWERTY!), translation problems (in the clip Mario kills a goomba by running into it) and page refresh problems (keep in mind, the Kindle processor may run NES games this quickly, but the ePaper screen could never refresh at anywhere near this framerate)—the emulator works perfectly!
In truth, the project seems more a proof of concept for KLab, a group that's built their own version of the Kindle Developer's Kit (KDK) and Kindle Emulator. The above clip demonstrates their NES Emulator running inside their Kindle Emulator. And should you want to get your hands dirty and try it out, they've shared the source code for all their projects at this link: [Google Code via Asiajin via CrunchGear]