After using the backpack for several weeks on and off the bike I still like it, but there are aspects of the bag I dislike.

The waist belt should be detachable. I just got back from a trip to SF, and I didn't have a bike while I was there. My primary means of transportation were muni and walking, so the waist strap was just annoying most of the time. The lumbar padding is essential to the design of the bag, but if the waist strap threaded through that, being able to take it off would be nice.

Due to the suspension system frame of the backpack the rear inside portion of the bag is curved inwards. I don't like it, but it's unavoidable because of the way the suspesion system is designed. Unlike a messenger bag or messenger-style backpack you can't pack this bag to capacity if you have a lot of heavy things with rigid shapes. I bought a couple school books yesterday which weighed about 20-30 lbs (roughly 10-14 Kg). They made the bag difficult to close, distorting the shape of back panel from curved to flat (basically flattening the spring steel frame). This made it extremely uncomfortable on the bike because there was a piece of the frame pressed against the middle of my back.

There are redeeming qualities I've noticed too.

Adjustability is superb on this backpack. The above picture of the velcro strap under the mesh panel shows that the bag can be adjusted to fit a wide range of people. I previoulsy stated (incorrectly) that this strap tightens the mesh on the back. That strap is actually connected to the shoulder straps, which are thread through a part of the frame. It is used to adjust the shoulder strap length in conjuction with the front shoulder strap ends. Although it's not something you need to change after you find a good spot for it. The mesh panel is actually tightened or loosened with a horizontal strap attached to a buckle that can be found underneath the lumbar padding.

I still haven't had a real oppurtunity to test the bag's waterproofness. I was in a light rain with it and nothing got wet, but like schnee said, you could probably submerge this thing and it would be fine. I just went outside, turned on the hose, and soaked it for about two minutes. There wasn't any water inside afterwards.

The suspesion system works well while riding. It's not amazing, but it does alright. After getting off the bike it provides a considerable difference. When I've just finished riding is usually when I get the sweatiest because my body is trying to cool down, but there is no more wind to keep it cool. While I was using the backpack in SF my back never got soaked in sweat like it would have with a normal backpack. I did still get some sweat marks on my shoulders and lumber region (where the paddding is) on one occasion, but I was running / rushing to meet someone when that happened.

The mesh helmet holder in the bottom pocket is a nice feature. I used it to carry a light package that was too big to fit in the bag one day (not it's intended use, but it worked well). The helmet holder can be left out all the time too. It won't interfere with the rear pocket too much because the pocket opens vertically.