I have noticed a similar thing - I don't see a MAC address until after I have turned wifi on. This only happened after the 1.2 update, previously I always saw the MAC address when first turned on.
I'm having a similar problem with my Color Nook.It worked perfectly with my network or with any outside location with wi-fi access for first several months. Then I started having intermitent problems with wi-fi not connecting. There was no rhyme or reason as to why it would stop working and then a couple days later work again. A few days ago it quit working altogether. I've tried turning wi-fi off and now I am unable to turn it back on. I get a caution sign that says "Wi-Fi issue". Under "About your Nook" the Wi-Fi MAC address is listed as "unvailable" .
I've tried all the normal stuff like resetting modem and router. Both work with all my other devices. I'm not sure what to do from this point forward. Because of the intermitent problems I'm inclined to think this may be a hardware failure rather than anything to do with software or the router or modem. I really don't want to reset/register as I really don't want to lose everything that is on the Nook. What a pain.
Any ideas on how to resolve this problem?
Make sure "airplane mode" is off then you can turn on wi-fi