There are several one-pound ultralight sleeping bags on the market now. My own is 17 ounces. It actually weighs 19 ounces with the stuff sack, but stuff sacks aren't always necessary. It can be stuffed directly into my pack or put in a half-ounce bread bag. It's a down sleeping bag, and has kept me warm down to below freezing - warmer, in fact, than my four-pound bag used to keep me.
It appears fragile, and I've babied it over the years, but it may be tougher than I thought. I've used it from sea-level to 16,000 feet, in all types of weather, usually camping under a tarp, yet it still has its loft, and it appears almost new. The zipper goes only half-way down, to save weight, and it's a mummy bag, but I'm 6'3", 165 pounds, and I've always been comfortable in it.
Sleeping bags weighing around a pound are summer bags, rated down to 40 to 50 degrees fahrenheit. A quick check of the newest bags out there, though, shows that even one or two of the 0 degree bags are under three pounds now. These are down filled bags, of course, as down is still the lightest insulation for its weight.
Another big advantage of any down sleeping bag is it's compressibility. Nothing packs smaller than down. However, a good synthetic bag is probably better than down if you are regularly getting it wet.
Several sythetic-fill sleeping bags now come close to down in their warmth-to-weight ratio. At least one summer bag, using Polarguard fill, weighs an even 16 ounces. That's amazingly light for a synthetic bag.
Using Ultralight Sleeping Bags
Ultralight sleeping bags generally aren't tough. The lighter the bag, the more fragile, but treat them gently, and they work fine. I've used mine for many years, in snow and rain, from Ecuador to California to Michigan, and it shows little wear. Baby these things, and they can last a long time.
