being very new to Aikido (1 month), of course I know absolutely nothing, but I have been observing the dynamics between myself (a woman) and the other aikido practitioners, both male and female.
The only person who has bruised me during practice is a woman, and it was the very first time we ever practiced together!!!!! She was testing my mettle. Or so I assumed from her facial expression and other body language.
Sometimes the guys (some of them) get a little soft and mushy around the eyes, and I know that they in some ways limit their aggressive acts because of their soft mushiness. I don't mind that unless they start aikido-ing in a useless way. Then I withdraw somewhat until they regain sanity.
Personal philosophy: I think that you can practice anything and have fun at it. (fun can include low-level flirting, ie/ mushiness around the eyes)
There is a male rookie at our dojo as well, sometimes I see a little extra force being used against him when he's uke than when the same nage is squishing *me* into the mat. Maybe it's just that particular guy, maybe he emits some sort of "beat me up" vibe. I have never been beaten on in my life, I don't think I emit that vibe.
Overall I have not noticed any interesting levels of sex-specific discrimination. People are easy on me, or slow and deliberate anyway, and I don't think it's cause I'm a girl but rather cause I am me.