I'll echo noam's comment. I've tried checkpoint friendly bags (a backpack and a messenger) and found there wasn't a lot of advantage. In both cases, the effort to open and layout the bag was as much as it is to pull my laptop sleeve out of my much lighter everyday bag.
Another thing to consider the the overall utility. Will you be travelling be air frequently (I fly 2-3 times a month)? If not, then most of the time the added weight and complexity is wasted. The backpack that I tried had a much smaller overall carrying capacity than a normal backpack while being quite a bit heavier. The laptop compartment was heavily padded and had an added all around zipper. Given the limited amount of time that one is being examined, it just didn't meet the overall function test. I want to spend my weight carrying budget on my stuff, not the bag.
I use a nylon covered neoprene sleeve from Built NY with a screen protector between the keyboard and the display (I've had laptop display scratched by the keyboard when they get compressed in an over packing situation).