Biggest Con with Nook books (and eReaders in general) is publisher-forced restrictions. Think about a paper book: You buy it, it's yours for life if you want. Shelve it, keep it, give it to a friend, sell it to a used book store, stick it in your attic, whatever. In 20 years, it'll almost certainly be there if you want it. If the store you bought it from goes out of business, you still have it. If the publisher loses the rights to it, you can still find a copy of it (most likely) in the used market.
eBooks are different. In many ways, the argument is the same with CD's vs. iTunes - physical media has some drawbacks, but versatility and logevity tend to be higher with physical books, music, etc.
Now, I love my Nook. A ton! I am now an eReader for life. However, it does concern me greatly that in some ways I'm not "buying a book", rather, I'm purchasing a limited right to read the book on the device(s) authorized by Barnes and Noble to read the purchased book on. I think B&N will have a long, successful life. However, what happens if they don't? Those books may sit on my current Nook, but what happens when the Nook dies (as all electronics do eventually?) Will I be able to download it onto my next eReader? Probably, as long as B&N is still allowing it, and as long as I get the B&N-supported eReader.
So, we ultimately trade convenience, portability, and the other benefits of eReading in exchange for long-term control of our library. I don't mind doing it, but I hope I don't regret this someday when I have years' worth of books I've purchased in a format that is restrictive and unable to be shared in any way I want to share it, as I have with paper books. There's just something long-term about a "real" book that disappears in this digital world. The publishers and new book sellers probably love the current market because of this, but we are giving up something pretty important as consumers, and, ultimately, as a society.
