It's best to get a SD card for non B&N items.
I have had my Nook for almost a year and have found an easily avoided glitch. A few times I have tried to do too much to fast (open and close too many apps or books). As a result the Nook has frozen and needed to be powered down and re-started. It's not a big deal to me because I want to be reminded that this is for reading, not playing. However, each time this has happened I have lost all non B&N data - pictures, files and books - that have been stored on the Nook. Data stored on the SD has not been lost. Since all my non-B&N stuff on my Nook is also on my PC I've been ok.