FYI, all modern Nooks run Android. The original model ran a proprietary system, but the modern Nooks are all Android and Barnes & Noble even has an unofficial policy of helping people root the tablets if they want to.
I'm aware (my girlfriend owns a color one), but they still run their own proprietary software atop of the OS, in addition to providing DRM-infected eBooks (but you have the option to put your own eBooks on the device, which can be DRM-free). Their TOS also states that they can remotely access your device at any time (stating that the act of doing so to apply upgrades may possibly harm your device), among other details I do not want to begin ranting on here.