So far it's not getting any worse but these latest shots are of the "inside" of the back and there are no dark spots... which to me means that the nook is not overheating or causing this from the inside out. This is happening from the outside... or rather from beneath the rubber-like layer on the outside of the back shell. 
However (in the latest shots), the very last picture is of the back cover (outside) and shows the discoloration on the top corners... a little hard to see but my previous images show the defect in decent detail.
I sent B&N Support an email yesterday... giving myself one more day to make sure this is truly a defect. If I don't get a reply back by 4:00pm today I will give them a call.
Yeah quite a bit of news really... sorry I didn't post any updates. I was a little upset.
Short version: I submitted a claim to the Better Business Bureau
Long version: I called many (MANY) times, each time waiting over 45 minutes before I gave up until the last time where I waited over an hour before finally talking to someone who just sat there in silence for most the time. He definitely lied to me (flat out none the less) by saying (initially) that his system would not allow him to send out "just" a new back cover: that I had to send in the entire device and would receive a refurbished unit should anything be found wrong. I told him then I expected a discount because I "paid" for a brand new one and had only had the Nook for a few weeks. He kept on saying things about normal wear and tear and blah blah blah until I finally (and forcefully) explained again that the Nook itself was fine and that only the back cover was damaged. He then proceeded (after about 30 minutes) to say that he needed my serial number in order to ship out a new back cover. LOL
At this time I thought... great... now he's BS'ing me like I'm a retard. But I didn't care anymore so I gave him my SN and said to hell with it. I then submitted another claim online and received another response after about a week stating that "this issue is one that is better serviced over the phone... please call [insert the same F'ing 800 number here]. So I wrote back telling them that I would NOT call the number again and demanded someone from BN to call me. Guess what... they actually DID! hahahaha
I finally thought I was getting somewhere and this new guy was a million times more professional and respectful.............over the phone. He told me there was no record of a phone conversation or my serial number anywhere in their databases (plural): meaning the first guy lied and this is proof. But then he went on to explain that he had never heard of this issue occurring with any other unit and that he "frequently" visits these very same forums. There are a LOT of threads in here so yeah I could buy that I suppose. He took down all my information and said he would look into it further and call me back with some options...
(I forgot to mention that before he called I received another email that gave me 3 options... receive a 10% discount, return for a replacement, or return for a full refund). I chose 10% which would have been enough to just purchase a new back cover when they become available again.)
2 weeks and counting... he still has not called back. Big surprise there!
I then received a response to my email choosing the 10% option that (again) stated: "This issue is one that would be best serviced over the phone... please call..."
I completely lost it at that point and perhaps even responded with some unkind remarks. LOL It's not like it would do any good anyway... they apparently take canned responses VERY seriously!
All in all... I love the Nook but absolutely HATE B&N customer service... I would rather spend hours on the phone with AT&T or Verizon. But of course none of that really matters anymore. Apple (IMO) effectively killed e-Ink technology. Proof is in the rumor that Amazon may decide to switch from e-Ink to standard color displays with their next Kindle and the fact they purchased a new color multi-touch (pressure) screen! Mark my words... if a color e-Ink display doesn't come out this year, it will never happen.
I'm bummed to hear your issue wasn't resolved. I just contacted them by email (I won't try the phone support after stories here about the waits). Mine looks IDENTICAL. Did you by chance ever use the brown javoedge sleeve or any other brown case? I'm using the javaodge "hardwood" sleeve.
I have the problem on all four corners AND a line going up the raised beveled edge. Seems all the "raised" parts are where the browning has occured. No I don't smoke, work in a coal factory, or use the nook with dirty hands. Even if I did that shouldn't cause this after a few weeks of use.
Seems like this is a product defect?
Exactly. Imagine if B&N support gave us direct updates on the forum -> gasp
I suspect this is a "case" of potential product problem brought on my the use of a tight sleeve that rubs the material each time you put it away. It's a very soft, but tight fit on this case and suspect it's wearing down the back. I suspect JAVOedge would say, bad material and B&N will say, "bad sleeve, don't do that".
I guarantee you it is not any 3rd party protective case at fault. I put the nook back in the packaging it came in when not in use... so basically "nothing" ever touched the top corners anywhere near enough to warrant discoloration. It is the fault of B&N only and the quality of their own back cover. Doing some more research online, there seem to be TONS of people experiencing this issue. This tells me that 1. B&N lied about never hearing about it before, 2. They did NOT take the backs off their website because they were "out of stock" when there are plenty of other back ordered items still up for sale, and 3. They're obviously not going to do anything about it... at least not for those of us who are having the issue right now.
This was just a very minor issue they could have easily solved... but now they're flat out lying to people and coming up with stupid excuses and runarounds. I'm not "too techy" for my own good either... in fact I've stated numerous times that the nook itself (as a device) works perfectly fine and I'm not mucking things up on my own. I'm not voiding any warranties or rubbing the damned thing so hard as to generate any discoloration.
In fact, readers... if you want the best eReader on the market today without spending a TON of money, get a Nook! Just be prepared for WWIII if something goes wrong. Still haven't received a call back by the way. Their customer service is quite literally the single most worthless service I have ever experienced in my life... regardless of whether or not one reads the user's manual!
Seems we can't blame a specific 3rd party or just the "air" for this problem? ROFL!
I contacted B&N and was told this was simply "wear and tear" and NOT covered. B&N, you have users on this forum telling you about a potential product defect, there are pictures, information about usage, etc.
Why setup a social site to engage with users and not use the information provided to your technical support staff. I pointed support to threads on this board and others and they still claim it's just "wear and tear". You can't blame the case breaking down on wear and tear when we've had the device for < 6 weeks and have provided evidence of multiple users.
Ok, I admit it; after long reading sessions i use a fine grit sandpaper to wear down the coating on the case because i love the "brown stained look". (JOKE)
Come on B&N - step up to the plate here and help out your customers! 
