I think in the end (as with most things), there are two extremes and everyone else falls somewhere in the middle.
There are people that are SO obsessed with not stifling their children's natural inclinations that they allow their boys to wear dresses, skirts, make-up and whatever else in public.
Then there are people that are SO obsessed with making sure their boy is as masculine as possible that they freak out over the tiniest display of "traditionally feminine" behavior.
To me, both extremes are very sad. Because SO much is lost when a little boy can't explore his nurturing side and is taught to be rigidly masculine above all else. Just like there is so much lost when a little boy isn't encouraged to emulate masculinity through a positive male role model....when they don't learn to appreciate the differences between men and women.
I think the best we can do as parents is try to keep things balanced. It is certainly okay for a boy to play "house" with his sister and perhaps even have a babydoll that he pretends to care for. But it's also okay to tell your son that dresses/skirts are for girls and no, they can't wear them in public... (playing "dress-up" at home is a completely different thing).
It doesn't make me a neanderthal for not allowing my son to dress inappropriately, no more than I'm a neanderthal for insisting he not go naked in public or "adjust" himself through his pants. These are social behaviors that we teach our kids every day and there's nothing wrong with that.
I honestly wouldn't buy my son a female Barbie doll, either, or sign him up for ballet class (though I could make an exception on that one if he was truly interested). I wouldn't buy him a princess costume or allow him to wear one for Halloween. But I wouldn't bat an eye if my daughter wanted to play flag-football or buy an action figure or dress up as a pirate, etc, Are these double standards? Sure, but so what? Not everything nowadays has to be genderless and sometimes what's okay for a girl to do is NOT okay for a boy to do and vice versa.
What's important is that we use our common sense in each individual matter and not be influenced by all the "extreme" opinions or social trends out there. To put it succinctly: Let kids be kids, but don't be afraid to guide them.