My girlfriend Gwen got one of the super-ultra-light G4 packs by GVP (as used by ‘Flyin Brian’ in his triple crown hike).
It is truly an ingenious pack. It takes all the lessons of the Go-Lite Breeze and goes a step further. It is a 4000+ cu pack that looks like 3000cu pack and has a waist belt (which many of the ultralights don’t have) and still comes in at 16oz.
The most ingenious part of it is that it uses a Z-Rest sleeping pad as the “frame.” This feature is shared with the Go-Lite Breeze but the G4 allows you to load it from the outside of the bag so you don’t have to unload everything out of the way.
The other key advantage is its configurability. The straps are set up to allow you to add only the bare minimum of foam (or unused clothing) needed for your body type. And you have the option of ordering it made to your specs with various loops, dividers and pockets according to your preference.
The real proof of it being a great pack however is that even with the pack loaded down with camping and climbing gear Gwen, weighing in at 120lb, said it was the most comfortable she had ever worn. (She was a bit skeptical of the whole thing at first and thought it was too light to work at all.)