"I too wonder about this, but also I'm concerned about the durability of ultralite equipment. This summer I set out with my new tarptent and light pack. Within a few days the pack had many holes in the bottom, and on a windy evening, the tarptent (which held up well, btw) really took a beating. The next morning there were holes in the thin, sylnylon material.
My sylnylon rainjacket also got a few holes in the back which I repaired with ducktape. But will it hold up?"
What the hell were doing with this stuff? Were you anywhere near a campfire?
I've got UL gear that I've had going out for three or four years now and it looks pristine. Along with UL gear goes some UL education -- you just don't beat this stuff the way you did the old 1000 denier Cordura. I had to explain this to one goofball friend of mine, who stuffed all his old heavy gear into a 14-ounce pack, complained about how his (38 lb) pack weight was just uncomfortable in this thing and then, at one rest stop, tossed it down, sat down on it hard and blew out a seam. We spent a season re-educating him, and since then he's been just fine with his own UL gear.
Will it hold up? Yeah, it holds up just fine if you treat it well. I know people that have had Stephenson tents for 25 years and more, and that's one of the early leaders in very lightweight gear.