I got my copy of Mastering the D90 from Amazon.com a few years ago. They still have it and now it is discounted for $23 and free shipping which is a good deal. Amazon says they have 16 copies left. It's a great reference book to have. It is a soft cover book with glossy type pages so it will hold up for the many times have looked through it and is very well put together with screen shots of the actual menu screens. It's definitely worth every penny.
"Old phones are like old people, not in style any more but still work fine."