It's not OK to hit anyone.
Hypothetically I don't believe it's any worse to hit a woman than to hit a man. I mean, there's some fierce chicks out there that fight harder than a lot of dudes.
There was actually a documentary on TV in the UK a couple years back that dealt with the topic of domestic abuse, but of women that beat their husbands. It almost never gets reported because of the stigma/ego/whatever of the guy.
I mean, shit, if any of you guys were in an abusive relationship would you call the cops or whatever on her? I doubt I would. But it's got to really suck for the guys that happens to, because if they do anything in retalitation, they're automatically the bad guy because of how seriously the police treat domestic abuse towards women. I don't know how the police would treat that situation but it seems like a guy could punch a girl once and be seriously fucked, but a girl could beat the shit out of a dude and it wouldn't get treated as seriously. I could be wrong, but that's how it seems.