The meat of the discussion in this thread has been very interesting, and makes me wonder whether I'm a) living in the right state, b) oblivious, or c) just really lucky: so far, I don't think I've run into any sort of gender bias or harrassment of any sort in any of the four dojos -- aikido, karate, jujitsu -- I've trained in or several I've visited. (Well, since visits last just a day or two, it might be harder to notice something subtle there.) I would certainly notice if someone was touching me inappropriately, so I know that hasn't happened. My two main dojos (aikido and karate) both make me feel very comfortable and don't treat women any differently than men. Same goes for the karate/taiji dojo I go to fairly often.
I probably have a pretty thick skin, since I'm an electrical engineer from the era 20 years ago when the male:female ratio in the field was worse than 10:1. But it's not THAT thick -- small slights from casual encounters I can ignore, but if I faced it regularly from dojo mates I'm sure I'd notice it. I have definitely seen and recognized bias and harrassment in "real life," so I know it exists and it makes sense that it would be in some dojos, too. I'm guessing it must be the tone set by the sensei: if he treats women the same as everyone else, others are more likely to; and if someone is out of line, a good sensei (meaning observant and right-thinking) would correct or remove that person. I never witnessed such a correction/removal in the dojos where I train, but it might have happened while I wasn't there.
As for makeup of the dojo, it's true that having women in it makes it easier for other women to feel comfortable joining. I'm glad to be doing my part to help the ratio. In karate, I coach the kids' classes (which are about 50-50; even the teen classes are close to that) and it's obvious that the girls identify with me -- the male teachers are great and the girls learn just fine from them, but it always helps to have a role model.
But much as I want women in the dojos and teaching at seminars, I would hate any sort of reverse discrimination -- this goes for the martial arts world as well as the engineering world, and in fact all aspects of my life. I would HATE not knowing whether I got a promotion/position because I was good enough or because I was filling someone's quota. I want all the males to know that I got where I am because I'm as good as they are. I've definitely felt at times in the engineering world (college and jobs) that some of my male colleagues are sizing me up deciding whether I was a quota-filler or not, and if I hadn't been very sure of myself it would have made me feel awful to face that doubt.