I'm sure a 4.0 will be around eventually for it. I've had a lot of fun with Cyanogenmod on an NC. The only con possibly being that they didn't hook up the BT antenna in the thing or something, but you can get an earpiece bound to it from like 6 inches away (now that's some near-field communication!)
I'll add the bigger problem with CM7 is the battery. My factory Nook Color could go a week or two between charges. Picking it up and just reading a book or browsing was never a concern. Now that I'm on CM7 there is a 50% chance the battery will be totally flat when I go to pick it up.