I see a few women in my age group (forties) wearing casual dresses, but only in the summer months. I definitely see more shorts, jeans and yoga wear on women of all ages.
I think there are several factors that affect whether or not you're a dress-wearer. There's the issue of how much they suit your figure (which makes it a lot easier to find dresses that fit) as well as your style sensibilities. For example, my best friend wears casual maxi dresses quite often in the summer. She likes them because they flatter her pretty pear/hourglass figure -- even the jersey ones that tend to look horrible on me! -- and they suit her romantic sensibilities. She is a womanly woman, not sporty or gamine in any way. She also says they are cooler than shorts, and they hide her thighs.
There's also the fact that the city I live in provides an excellent example of North American casualization. It's ground zero for LuluLemon. We are known in Vancouver for having no style!
I wear dresses when I attend a wedding. That's about it. Even for funerals, it's always a skirt and top, not a dress. But I'm a boy-woman, both in shape and in attitude, so even though casual summer dresses are pretty and airy, I have never had the urge to buy one.
