I bought this bag to use as my only piece of luggage during a 2 week trip to the Czech Republic.  It was absolutely perfect, and later in the summer I also used it to tote everything I needed for 6 weeks in Michigan.  It holds enough clothes for about a week (I had planned on doing laundry halfway through my CR trip, so that was just fine), along with toiletries and what ever miscellaneous other things you need for your travels.  I had plenty of room to spare, which was good since of course I came home with more stuff than I left with :)

As described in the product info, it's the max size for carry-on luggage and I had no trouble at all bringing it with me on the plane.  The straps tuck into the back compartment even when the bag is CRAMMED full, making it much easier to slide into overhead compartments.  The two straps that go across the front of the bag are also really useful--they're adjustable which ensures the contents stay snugly in place.

There are just enough pockets, and all are arranged in just the right places.  The pack opens like a suitcase and the inside is kind of designed like one, too.  There's a mesh zip-pocket lining the inside front flap of the backpack, as well as another smaller mesh zip-pocket inside along one side of the bag.  The pocket at the top of the bag, accessible from the outside, is handy for stowing your wallet, tickets, a small travel book, etc, while the larger external zip-compartment along the front is good for larger flat things like a folder or map.

I'm pretty short (5'1") but found this bag comfortable to carry for short periods of time, even when completely full; the straps are well-padded and fully adjustable.  It holds A LOT and can get quite heavy.  I was just amazed at how much stuff I could fit in this bag.

Overall I'm very happy with my purchase.  This will be my primary traveling bag from now on, and I look forward to buying another, smaller, Osprey bag for commuting.