Pete Lovejoy wrote a review of Osprey Packs Atmos 50 Pack - 2800-3200 cu in on March 23, 2009
I have been using this pack for about a year now and personally I love the way these packs fit, they are very light and comfortable with tons of features. I sweat a lot in summer and although the design of this pack won't stop that (only cold weather can do that), it reduces it a lot! The only thing I can think of that I would like that this pack doesn't have is a daisy chain or more places to attach things to the back of the pack (and that is mainly because I use it for winter as well as 3 season).
I have three packs, a multi day pack (which I got before I found Osprey packs and can't justify replacing), the Atmos 50 and 35. Each has their own place, I use the 35 for most hikes and the 50 for light overnights, winter day hikes (not what the pack is for, and although it works it isn't what I would recommend) and hikes where I want to bring something that takes a lot of space (for example I once took ice cream to the top of a mountain and I needed the space to fit the cooler with dry ice as well as the usual gear). This is usually overkill for light day hikes and it isn't large enough for multi day trips unless you are a real minimalist.
You should go and try an Osprey pack at a local shop to make sure you like the feel, some people like the way that Gregory (or some other brand) packs fit better, but if you like the feel you will love this pack!