The Atmos 50 has become my default backpack. In the summer, the ventilation is worth every added ounce. The pack is about a .5 to 1 pound heavier than comparable packs, but it carries (on me at least) very comfortably, so I don't mind the extra weight that much. It's a little odd to load, but I figured out the best way on my first day out.

I wouldn't use it for winter though.