Another 2 cents worth: I think it depends on the woman's coloring, including hair color, her job or profession, and the percentage of gray hair. Hair type is also a consideration.
When I started coloring my hair I thought it would be for just a few years until it turned mostly gray. I thought by my current age I would have stopped coloring. Well, my hairdresser tells me it is still less than 20% gray. My original hair color had a lot of red in it, and it is my observation that women with similar hair color don't look good with gray streaks or part gray hair.
One of these days I will try on a few gray wigs, because I don't know how I would look overall gray. Luckily keeping it colored isn't that difficult or expensive--roots every 4-5 weeks, lowlights every 4-5 months, and an extra half hour sitting at the salon catching up on People magazine.
Every so often I see a woman with long (below shoulder length hair) that is part gray and doesn't seem to be in good condition. That is unattractive, and IMO it looks like she doesn't care.
And yep, a professional or business executive male is usually enhanced by graying hair, where a woman in the same position may need to look younger and sharper. The world just isn't fair that way yet.
One more thing, my DH, who just turned 70 and has relatively few gray hairs, is far more creeped out by it than any woman I have ever known. He still asks me if he should dye it. I always tell him he'd look strange--most older men with all one-color hair look weird to me. It's easier for women to do it, probably because we are used to it.