I have the Granite Gear Virga, which is much lighter:http://www.granitegearstore.com/Virga-P6.aspx
I've used it extensively. After much sliding down anorthosite steps in the Daks, it's showing some wear along the bottom. However, it's certainly not in danger of falling apart on me and spilling its contents. At some point I'll need to add some patches, but I'm quite happy with the durability.
Comfort is excellent. I have carried up to 25lb in it, using a cheap ($6) foam pad from Wal-Mart as a "frame". By putting this pad (cut down to half-length) around the inside of the pack, it protects my back from pointy objects, provides lots of support, and also makes the pack stand up on its own and holds it open when I want to get stuff out. I tried a folded Z-lite as a back pad and it was not even close to as comfortable. With loads up to 25lb, this is every bit as comfortable as the most padded full-frame packs I've tried. Above that the thin wait strap begins to be a limiting factor. The heaviest packs I ever carry are 40lb (guiding or multi-day alpine climbs), and even then I find no use for a more rigid framesheet than a foam pad. A properly designed (and loaded) pack will transfer weight to your hips just fine without one. My heaviest pack is about 3lb (Cilogear 45L w/o framesheet).
It doesn't offer a good external crampon carry system, but the axe holsters are fine, and I've strapped trekking poles to it without issue. When the climb is going to be highly technical I bring my Cilogear packs, but if it's really just a backpacking trip this is my go-to pack. I can't imagine going back to a regular frame pack now that I've seen the light(weight).