From what I'm seeing, it appears to be the UK Nook Store App for now. Here's the official UK site's announcement, complete with a link to a FAQ: http://www.nook.com/gb/notice
My nook devices and apps -- U.S. -- are working and I haven't gotten any notices. I'm not sure nook ever really got a foothold in U.K. I hope the U.S. nook stuff isn't ending. I've gradually weaned myself from kindle to nook and nook has a good academic foothold for textbooks on the local campuses. If it happens, I suppose I'll be stuck with backlit on demand options like U.K. shutdown then just go with kobo for new purchases. Some other U.S. devices shutdown but migrated to kobo; ideally nook would work out a kobo deal if shutting U.S. nook (and would be kicking themselves for spending huge sums fighting off Microsoft's attempt to gain nook as competition for google Play and iBooks).
Thank you Debbie for the information. I can see why its so good for you. I hope the rumors aren't true. I still haven't seen any other information other than what I've seen so I hope its just one of those things that go around.
Thank you Kate.