I've got a pretty ok carry-on, but it's made out of a heavy vinyl type material. Mostly I just travel with an old army knapsackl though if the trip is short. Last year I was walking past a luggage display and I reached out and lifted one of the ultralights. Holy hell are those things light. It felt like I was lifting a Sunday edition of the New York Times. Since then I've been mentally weighing the return on investment I'd get by buying a new ultralight carry-on vs just using what I've got, since I travel kind of a lot. Like thenewgreen, I refuse to check bags because there is only a downside. With more and more airlines putting a weight limit on carry-on after which a charge is triggered, the lightest possible container makes sense, esp when you are fitting all of your gear for your trip into it. I'm thinking a beat up used ultralight would be the best of all worlds, because even though it will be with me at all times as a carry-on (hopefully), I'm a huge proponent of carrying used/shitty looking items when they are ripe targets for theft. My knapsack has one shoulder strap that is broken and no longer adjustable. It's knotted together, which I approve of; it looks like the last place you'd find anything of value...good to carry my laptop because it doesn't telegraph having a laptop pocket or anything like that. That being said, a lot of thieves are just idiots who will grab anything.
Truth is the guy with the old army knapsack in the overhead compartment is likely taking up more space than the guy with the roller bag. It's just not designed for that space, and the roller bags all are. No manufacture of these bags would ever design one that couldn't fit up there easily and efficiently. I use mine all of the time, and not just when I'm flying. I use it when I travel by car because it's easy to roll through the hotel etc. I highly recommend it.