I don't treat girl gamers any different, though maybe it's because I am one myself
I definately get treated differently; creepy people will always stalk you in the games (especially mmos) and those who feel emasculated often imply I'm bad at games because I'm a girl (Nvm the fact I've been playing games my whole life, and without being boastful I am good at most games).
Sometimes I'll make a male character if I want to avoid all that hassle, and I usually get treated with more indifference and respect equally.
I can think of 2 instancess in particular which were pretty funny:
The first and most recent was on Street fighter 2 HD on the 360. I was playing online matchmaking, but only a few people were on. This guy kept beating me everytime I played him, until about the tenth time i fought him, and I managed to win it. Imediately he sent hate messages (I'd only won one match lol, wtf), and wouldn't stop, until he realised from my avatar I was a girl...
Then he sent me a friend request. Needless to say I ignored it and blocked him.
The second example was a long time ago; I used to play Jedi academy multiplayer, and joined a clan. They had a trial period which they used to assess your character, and when they felt you were ready they'd teleport you to remote part of the server and watch your jedi trials lol.
I needed to fight a Master, a Knight and an Adept in that order, in order to get my apprentice title and be fully accepted into the clan, it's not expected to win any of the fights, rather to see how you cope against each challenge.
So the fight with the master starts, immediately I leap in with the Strong lunge attack, an attack so slow and easily dodged barely anyone ever used it... but it worked, and killed him in one hit.
So they were surprised but let me fight the knight. This was much closer, but I managed to win again. So there I was all ready to fight the adept, having already won two rounds, when I get a tell from the master 'You have failed your training.'
Of course I was confused as to why... turns out they reckoned I'd been cheating because (in their words) 'Girls shouldn't be able to fight aswell as men, they don't have the genetics.'
That was pretty much the end of my jka experiences.