I have had this notebook packback for about 9 years. It has traveled a lot and has never let me down.
Originally, I felt that this packback was overkill - but it has been able to accommodate larger and larger laptops (from 14 to 15.4 and finally 17 inches). Although not optimized for the 17 inch laptop (one of the retaining straps is too short), it really works fine.
It is constructed out of very heavy duty ripstop and other nylon-like materials. There are five external zippered compartments, and one zipper pocket within the primary compartment. Liberal use was made of nylon webbing to create pockets allowing visibility of their contents, and bottle or can holders on the outside. You can use the outside webbed pocket for your MP3 player.
There are multiple dividers within the compartments to organize papers, pen and pencil holders, ID card slot, and clip for keys. The computer compartment is very well padded, as are the shoulder pads and back. The molded carrying handle is comfortable, riveted, glued, and sewn in place. There is a detachable phone pouch, non-skid rubber feet on the bottom, and a waist band.
The zippers will allow the use of small locks on all except the smallest compartment. The primary and secondary compartments have weather flaps over the zipper, which are quite effect in moderate rain.
This pack has a large capacity and could easily carry a day or two's casual clothes in addition to the computer (throw a Eagle Creek Pack-It Cube inside). Its approximate outside dimensions are 19 X 14 X 7 inches (when fairly full). I don't believe that this particular style is available anymore, but Targus has a number of newer models which incorporate the same quality and features.
This pack has a lifetime warranty.