Not too long ago, XDA devs were able to bypass the bootloader for the Nook tablet. With that done, Android developer Brandon Bennet (aka Nemith) was able to sneak in a CyanogenMod9-based version of Ice Cream Sandwich into the B&N tablet. The Nook Tablet has already been rooted but the fact that the bootloader was locked, has made installing custom ROMs quite difficult.
Also in the works, are tools that allow booting the tablet directly from a microSD card which will enable loading Android 4.0 and other good stuff. This experiment is still a work in progress, meaning that there are features of the Nook Tablet that aren’t 100% operational but it is definitely a step in the right direction.