Well, I read boatloads of novels. And I always look at the maps and stuff of that nature. I read every word of the story, bu at the end when I get to the aknowledgements or something like that I ignore it.
It depends. Most of the books I own are fantasy or just instructional books, and the problem with a lot of fantasy writers is that, IMO, they tend to... well, drag things out a lot. Anywhere from characters and plots to simple descriptions. So I usually end up skimming huge chunks of text/paragraphs of d00m because of how insanely long they are. And I've found that a lot of newer books coming out really don't hold much of my attention anymore. I recently read one book that jumped between dozens of character groups randomly without any warning and was like, "wha--I thought I was just reading about X's group?" I never finished it.