I've had this guy for a couple years now and love it as a day-hiking pack. I've never carried weight as comfortably as I do in this backpack; it feels more like part of your body than it does like a pack. The Air Core is brilliant and keeps the sweat off your back (although you're still gonna sweat where the straps come around your shoulders) and works as a cool place to store your water bladder. The pack also has reasonably handy pockets on either side of the bottom of the pack for water bottles if you don't want your water tasting like a rubber.
As some other people have said, this pack isn't made for transporting books and laptops. Its curvature makes it remarkably comfortable, but not particularly good for carrying rigid rectangles. I can force my (15-inch) laptop into it -- and have -- but there's not much space left once you've done that, which I think limits its practicality as your school backpack, city pack, or business+pleasure airplane carry-on.
But when you're on the trail and what you got in there are your essentials, food, and rain gear, you don't really care about its incompatibility with your laptop. When it's in its intended environment, it's brilliant.