While not on this board, I know of a female GM who runs her game in Brazil. She claims that while it's not a big deal to have female gamers at the table in that country, it seems that being a female GM gets the "Uh, its a girul!" repsonse.
If I remember right, her history is that she was a gamer and then thought about GMing. So she got her best friends, all of which had never rpged before, and then ran her first campaign with them. That sort of made sense, everyone was learning so there was no pressure to meet anyone's standards. She now games a mixed group.
From what I gather, she has different styles between playing and GMing. For GMing, she does plot and rpg, for playing she likes to do over the top combat.
I also noticed that she has a low tolerance for any sort of player foolishness. If people start playing politics or having issues with her or other players, she just postpones the game until people decide that they can either leave or deal with their problems and come back to the game table.
For me, I haven't seen or had that many female GMs. Mostly I think it was the connection that most of the female players I had were g/fs to guys I gamed with. Their main motivation to be at the table was not the game itself.
As far as female to male rations changing the game play, I have the best story so far. I once ran a game of 4 players, both were couples. Then the two couples decided to break up and switch partners. That sort of tanked my project right there.