Want to mention one other thing. From what I have read on this forum and other places, having your Nook Touch, with its e-ink screen, turned on or sleeping is much the same thing. What causes the significant battery usage is PAGE TURNS and other screen-change operations.
So if you are a slow reader and have it turned on and are reading along slowly, you are not using much battery power. In fact, someone who is reading fast and doing more page turns would actually use MORE battery power. Also, having a larger font will almost surely use more battery power, since it requires more page turns.
This, of course, is only true with e-ink devices. Back-lit Nooks like the Color and Tablet use a lot of power just by being turned on.