....FTMFW!!!
Chris picked this up for me last week for my commute (since I take my lunch, a change of clothes and the contents of my purse in a backpack). Finally ot to use it today. Flippin outstanding pack. Not only does it organize and hold a shitload of stuff, it's got tons of reflective piping (it's still not quite light out when I leave for work), really comfy padded straps, and two straps across the front (one across the chest, one at the waist) to keep it in place.
Even fully loaded, it never felt like it was slipping, or going to come off at highway speeds, and the profile of it is low that I never once felt it *bump* my helmet or get in the way of moving my head or anything on the bike.