After having 2 girls I had a boy and it has constantly made me laugh how "boyishly" he plays with their things. When he was about 11 months he grabbed DD2 dolls parm and immerdiately turned it over to see how the wheels worked. He is just one of those boys that likes taking things apart and building things or playing with things with wheels. When he was smaller the main toys he had access to were his sisters and he still played with them in a completely different way to her. Now he is drawn towards cars and trucks and Thomas stuff. We have never pushed him into gender specific toys its just what he has chosen.
I really think a lot of it is ingrained in their personality regardless of how we treat them.