Hmm,
I run a game with a woman and two guys in the group and I don't think I'd really like it any other way. She doesn't particularly like the hack and slash mindset of one of the guys or the loot and pillage mindset the other guy has (Thank you Dragon Magazine for the Pillager's Handbook article, heh).
Like a lot of DMs I run a PC in the group too. Only have three regular players so that much needed fourth PC is run by myself. Something that aggravates the girl and I is the oneupmanship that constantly occurs between the two guys. This is a common 'problem' and a big reason my younger sister doesn't play with us (and won't let her fiance try it either), even though she does hang around and watch (and occasionally offers input).
I tend to try and balance our gaming sessions with slightly more story then combat. I find that both the males and the female actually prefer this to pure dungeon crawling, though you'd likely not ever hear either of the guys admit it.
In my opinions it's the totally unnecessary aggression and arguing that guys bring to the table that deters a lot of women. Most of the women I know are pretty aggressive though. A lot of them also like online RPG's and role-playing console video games. A few of them also really like movies and books with a high body count and lots of explosions. It'd be difficult to get any of them to really sit at a gaming table, however. The constant bickering and showing off the guys do doesn't sit well with most. It's also somewhat daunting for any new player to come to the table not knowing exactly how to play. Combine this with a few guys who know the game fairly well and absentmindedly berate the females and you have an unintentional "No Girls Allowed" game pretty darn quick.
As a guy myself I had really gotten used to the arguing and need to 'look better' in front of my guy friends. Now after DMing at a D&D/d20 Future game for the past few years I find it extremely annoying in any setting. Not that women don't do exactly the same thing, it's just their tactics are not as obvious. You could say DMing with a girl in the group has helped me relate to women and get along with them a lot better in general then I ever did in the past.
So I think that if an all male or mostly male gaming group wanted more females, both the DM and the players need to change their playing style ever so slightly. Work with each other a little better maybe. Rules Lawyers should quit being like that, and those who don't know things as well really should take a little time and figure it out. The few women that game should really encourage their female friends to give it a shot too. Good DMs know how to make things easier for new players, or at least we should (a small stack of pre-genned character sheets works well). I know the little folder I store dead character sheets in would be a little less thick if my players actually got together behind my back and worked out any kind of team plan for taking on what I throw at 'em. And many of my female friends would be a lot more interested in playing.
-Aaron
