One point to consider...
Although I have never had my carry-on bag weighed for domestic USA flights, there are international carriers that have (sometimes quite strict) weight restrictions on carry-on bags for the various grades of flights.
China Airlines states that their restriction for economy class carry-on bags is 10 kilos or about 12 pounds. This made me rethink about using my Lowepro roller case for my upcoming trip to China aboard China Air since the bag itself, empty, weighs close to ten pounds. That would not leave me much leeway for gear inside.
I have, instead, decided to use my Lowepro Mini Trekker AW for the China trip. It weighs just about 2 pounds and I can (with some judicious selection of gear) pack my two 1.6x camera and three lens outfit in a bundle which weighs under 12 pounds.
The Mini Trekker, although it is without wheels, easily rides piggy-back on my small wheeled suitcase to and from the airport and between hotels. After I have checked in the wheeled case, the relatively light backpack is easy to lug around and place in the overhead rack.
If ever for some reason, the Mini trekker should exceed 12 pounds, it would be easy to remove a camera and a lens from the case and carry it though check-in around my neck. This would easily reduce the backpack to the allotted weight.
Additionally, I have learned from various Internet chat sites that the China Airlines check-in folks are not quite concerned with the weight of backpacks but, are fairly strict in weighing roller carry-on bags. This could be the case or not. However, I want to be on the safe side and will keep my gear below the allotted weight restrictions.