I've had exactly the same experience. When I first got it, I was getting battery life very much in line with what was rated (30 hours total run time).
I charged to 100% this past Saturday, and this morning (Tuesday, so 3 days) after perhaps 5 hours of use, I'm at 36% battery remaining. WiFi has been off at all times during this (I never, ever turn the WiFi on, everything is side-loaded)
I also put in custom screensaver images (though I add text to the bottom of my screensaver images that says "This Nook belongs to xxxx xxxxx, phone xxx-xxx-xxxx"