Well, I went with Ectaco's (my Texas friends kid me and call it my extra crispy taco ereader
"suggestion" and read all books in .txt, I have an SD card only for the firmware updates, and use Calibre to do all my organizing, and only keep one page of books at a time on the JBL.
If you ever have a freeze, which can be a little scary at first, there are two things to try
using a looooong push of the power on button (3-5 seconds)
connecting the mini usb cord from JBL to pc