I really like quilts for moderate cold weather 20 F and up. (Below that and I like a mummy bag a little better.) IMO, the quilt allows you to cover a much wider temperature range than a traditional sleeping bag. On warmer evenings, you can drap only part of it on just enough of your body to take the chill off. Then it's very easy to pull over all of you as the night get's cooler. In colder weather, you can wear more clothes to bed and not worry about compressing your insulation like you would with a tight mummy bag.
If you backpack hunt, the ability to have a lighter quilt/bag and wear extra clothing to bed, if it gets cold really helps save weight and bulk. You can wear those clothes in the day when you are sedentary, so they do double duty. (Just keep those sleeping/warm clothes dry.)
The secret with a quilt is to get one wide enough so that you can roll on to your side with out your rear hanging out and getting drafty.
You can make your own synthetic quilt for well under a $100. For better weight and smaller volume in your pack, good quality down is the way to go. There are many quilt manufactures out there now.
I've got one from Enlightened and it is a good value and I like it. The RevX30 long model gives me 2" of loft, plenty of room (I'm 6'2" 175 lbs, weighs a scant 21.75 oz for under $200. With just long johns on, I'm comfortable (I consider myself a "cold sleeper") down to the high 20's. Add a thin wool shirt and a thin jacket and I'm comfortable into the high teens.
My "heavy" 4 - 5 lb mummy bags stay at home now for most trips.
Bill