There's no doubt the face of the gaming landscape has changed over the years. When I was a kid, right or wrong, gaming was considered a boy thing. Granted, everyone had that stray sister or cousin who wanted to play, but in the eyes of the world, gaming was like G.I. Joe...targeted toward the male demographic.
Now, you can take a look at many games today and see that the demographics haven't exactly changed (at least from a marketing stand point). We have more scantily clad females appearing in games these days than you can shake a stick at. However, you can't down play the influx of serious female gamers into the hobby.
According to Microsoft's COO Kevin Turner, gamers of the female variety now make up over 40% of its users.
Now, I'd be remiss if I didn't mention, right off the bat, that that number seems way too high, (boarding on unbelievable). The reason being, as I'm sure you know from your own experiences, the amount of time spent on consoles these days for non-gaming activities (such as watching movies via Netflix or Hulu) has sky rocketed. This is why the above stat fails to break down exactly which category the females “activity” falls into.
The good news is, with many innovative games on consoles like the Wii U and 3DS, games are becoming more and more accessible to not only your average, non-gaming female, but also to folks who never took an interest in gaming till now.