Daphna Joel published a report on this last year. Gina Rippon is also very good - and if you get the chance to hear her speak, do go; she's great! She's also on radio once in a while. She's worked a lot with Cordelia Fine. She (Rippon) has opinions about Baron-Cohen and Brizendine's work which are not supportive of them.
Gina Rippon says that there are differences between male and female brains, but there are far, far more similarities - if you plot abilities of brains on a graph, you get a bell curve for male brains and for female brains, and they nearly overlap, but not quite. I can't quote you sources at this time of night, but if you google for Daphna Joel, Cordelia Fine and Gina Rippon, you'll probably get links for the relevant papers.
One of the issues with studying brain differences is that brains are so plastic (as in they can change, rather than literally being plastic, obviously.) Linguistic studies on which bits of the brain light up when performing certain language tasks - if that bit of the brain is damaged though a stroke or accident, then with practice, the brain will forge new links and use other parts of the brain. It's not totally simple like that - some brain damage will cause permanent damage, depending on the area of the brain and severity.
But the point is that use changes the brain - like the example above with the London taxi drivers who do the Knowledge. It's why when you learn new things, they get easier with practice - there's that thing about the 4 stages of competence - unconscious incompetence, where you don't know just how rubbish you are; concious incompetence, where you have learnt enough to know just how much more you need to learn; concious competence, where you recognise you are good at the subject; and finally unconscious competence, where you do things almost automatically. If you drive, do you always have to think about changing gear, or do you do it because you are receiving signals from the sound of the engine, how smoothly the car is running and so on, which you're not fully aware of? Or touch typing, not having to look for the letters on the keyboard. That sort of thing is unconscious competence, and you get there by hours and hours of practice of whatever the skill is. The exact number of hours will depend on the person, how well they're taught, how much time they dedicate to it, and how often, but over time, your brain learns new path ways, and repetitive use makes those pathways stronger.
So, if your bedroom is painted pink, and all your family tells you girls like pink, and you're dressed in pink skirts, and you see a pink aisle at the toy shop, and the girls' things at nursery are pink - no one has consciously taught you that pink is for girls, but everywhere you go, the message is being constantly reinforced, in pretty much the same way that we learn the sounds of the language around us and so on.
It's also something which is quite difficult to research. It's not ethical to take a baby at birth and try to fix the input into their brain until adulthood, to see how they turn out, to work out how much is nature and how much is nurture - plus, unless you got twins and separated them you don't have a control, either (and not even then), because people do have their own personalities, and siblings who grow up in the same household with a lot of the same influences still end up different.