There's no doubt that social conditioning is insidious. My children are cared for primarily by their father but DD has absorbed the pink lessons and loves nail polish. I'm fine with that even if I am sometimes surprised at how prevalent it is when you consider that she doesn't even go to nursery or similar.
However, I do find it shocking that so few people question these things. That think DDs love of nail polish is genetic. FFS. Of course it's not genetic. It's because she's picked up on things around her and is identifying accordingly.
I'm not going to force her not to wear pink as part of a feminist ideal. But I sure as hell am not going to encourage it either. Both children are encouraged to play the same games, and by both me and Dh playing those games with them, they do. I will happily buy a little girl a "girlie" toy if I know she prefers it, but I don't assume that and, where I can, I go for toys that are more gender neutral. Girl/Boy party bags just boggle my mind - it's a bag of tat, surely a bouncy ball is a bouncy ball? why does it have to have a princess (girl) or superhero (ball)?
As parents, I think it's our responsibility to try to question the stereotypes and to teach our children to feel comfortable in themselves no matter what they're doing. But you can't do that if you don't first acknowledge that these exist and that our children are being pushed into certain types of behaviour because of longstanding social conditioning.
On a slightly separate note, for example, nothing makes me angrier than when I hear parents (usually dads) saying to their DS's: "You're throwing like a girl" or "you're crying like a little girl." It is so damaging to both boys and girls and yet is so prevalent. You hear it all the time.