I haven't made any bows for adults (that I know of!), but I have made them for teens. They seem to like the smaller bows that can be clipped into the side of your head, like a tiny baby clippie using 3/8 inch ribbon. I've also had some teens request the really big bows, like a cheerleader might wear with a ponytail. Those are usually about 5-6 inches across and double stacked.
Dove Designs Hairbows and More http://www.etsy.com/shop/sowega