Jeremy, not too many. Most cottage companies tried to go lighter than a half pound but ran into the durability wall.
A couple examples:
Old GG G5: Every trip out for a week would require some sort of repair when I got back. The spinnaker progressivly stretches, then fails. Especially the straps/mounting clips attachments. I eventually cut the lower sections off and replaced them with silnylon. I remember the pack weight was around 6oz or so for starters. But, I later deemed it unreliable for week trips and only used it for weekend trips. Eventually, I stepped on a rock that broke off and slipped down about 20' on a hill, tearing the bottom of the pack and pouch out. My daughter had the G5 silnylon, that held up pretty well. But the weight was around 8oz after beefing up the bad spots before she even took it out. She still uses this. GG no longer makes either of these.
The Whisper was nice because it was smaller. But again, had a similar problem in that the fabric progressivly went bad. Even with a sub-10 pound load.
The standard SUL/UL pack will be less than 1 pound. I have an older MiniPosa that weighs about 15oz that handles 25 pounds of gear easily. For two weeks out, this is more than enough.
Volume seems to be important. The Murmur "can" fit a BV450. Smaller sized cannisters, too, of course. This is my prefered pack for trips up to two weeks out. My base qear is fairly light at around 6 pounds. Food, however, is highly invariable. I need around 1.1-1.3 pounds per day for two weeks giving me a total food weight of around 16 pounds. Most of the SUL packs do not work well with a 22 pound load. If, I bring my saw it will be around 23 pounds. I assume you know that 15-20 pounds is the approximate cut off for SUL packs. Even the old G5 had a 15pound weight limit and this was pushing it. The total pack weight means I need a waist belt. Even a strap, as on the Murmur, is enough to pick up 7-10 pounds. Adding this to a Zero will push this over the 4oz needed for SUL, for me. So, I don't bother. The UL MiniPosa at 15oz works well.
Volume and Weight seem to be tied together. As a general rule, the smaller something is, the less it weighs. Small lights, small stoves, small fuel volumes, high density foods, two 500ml water bottles, a small grease pot, spoon, bear line/ditty bag, some vitamins/mineral pills, a lighter, a 17oz 40f bag, 9oz pad/pack frame, 14oz tarp, 10oz down sweater, long johns, socks, Steripen, bandana, rain jacket are about all I NEED. This comes up to around 4.5 pounds. Repair kits, first aid, spare batteries, etc. account for the rest. Heavier clothing sometimes in spring and fall(eg, a wool sweater.)
Cuben packs, like the Zero, are nice. But again, reaching the ultimate goal of 4oz on a pack and still maintain enough durability for week long trips is always a problem.