I had one of the early "ultra-light" packs that I bought in the States back when the whole ultra-light movement was starting. And there was definitely a compromise with durability to get the weight down. First the dwr was damaged by abrasion, and then the stitching on the peripheral straps failed. That said it had lasted 6 years even so. I would have thought they've improved durability since then though. The Montane packs aren't seriously ultra-light anyway, there are lighter ones with more compromises around.