I got a Nook Simple Touch from my wife as a Christmas gift. I have a Kindle too. I like both, but there are subtle things about formatting a book for them. For instance, on the Nook if an image is enclosed in paragraph tags it is indented on the left and the rightmost part of the image gets chopped off. Some images get chopped off at the bottom. The solution is to replace <p> with <div>.
Another thing about the Nook is that they put EPUBs from the Internet Archive in their Store for free, rather than getting them from PG. Of course the EPUBs in IA need proofreading, badly. I replaced a couple of EPUBs in my IA donations with corrected ones and those got put into the Nook Store automatically. Other EPUBs I donated, which were not connected to PDF donations directly, have not show up in the Nook Store, although I would not mind if they did.
James Simmons