I overthink when I buy electronic gadgets. I read reviews and test drive the devices. I ask friends and folks I observe using the device to share their experiences, good and bad. I look at the major players (Kindle, nook), rising competition (Kobo, Sony) and wannabes (Astak, COOL-ER). All this effort and I've only described assessment stage one.
For an eReader, I narrowed the field to Kindle and nook. I downloaded the eReader apps for both onto my lappie to see what the shopping experience was and how well book availability in eBook formats matched my reading wants and needs. For me, this turned out to be the most important criterion. I searched for titles, authors, and genre I'm most inclined to read (history, historical fiction, fantasy...) and found that Barnes & Noble stocks more of what I'd read on their elibrary shelves than Amazon by a fair margin. Having toyed with both Kindle and nook and finding little enough to distinguish one over the other, I purchased the nook.
The 14-day, "no questions asked if you return it" trial period gave me an opportunity to further convince my skeptical self that I'd made an informed choice and a good one. I was happily surprised at the diversity, number and quality of free eBooks available from Barnes & Noble. I expected most free offers to be romance, erotic romance, and, well, dreck. Instead I found books in genre I like and they were well worth reading. I took the opportunity to try the LendMe program and had a friend hook me up with one of his eBooks. This might seem like a trivial feature but I loan and borrow paperbacks all the time and it's comforting to know I can do this with my nook.
I should comment on the nook features, too. It's not an iPad so don't try to compare the two.I found that the nook WiFi is easy to configure and worked without problem with my Airport Express and with a hotel WiFi in DC. The web browser is without question limited, but sites without frilly nonsense like Flash work fine. [Hint: visit the mobile device site (ESPN.MOBI, MLB.MOBI_ versions of your infosites and you'll have a better user experience.] I "side-loaded" a podcasts I subscribe to through iTunes and some music and the audio works as well as any handheld. There's no security feature worth mentioning. Changing your account password or having customer service unregister a lost or stolen nook will protect you from unauthorized charges.
Bottom line. The killer app for an eReader is the eLibary. The device is secondary. The nook is simply the form factor that gives me portability and connectivity to the eLibrary that suits me best.