Many years ago I saw a pic of quilted curtains in a design magazine, but have never found a pattern or given it a try. The house I was born in was very old and cold in winter (England). My grandmother used to hang double sided curtains (velvet) to be drawn across the doorways, sometimes I know she sewed a flannel sheet in between for extra insulation, but never quilted them.
I too will be watching this post. With utility prices rising again, and having a house with lots of big windows, I can see quilted curtains are going to be in my future.