my nephew had a great (girl) friend from when he was about 2. They were really close until they both starting being interested in the opposite sex - 13 or so. I guess they were more like brother and sister
He isn't a particularly boisterous boy and whilst I can't imagine him playing with Barbies, so far he has plenty of stuff he likes doing which are not solely boyish things (major gender stereotyping going on here - apologies).
My DD is 11/yr 6. Recent party, almost half her guests were boys - and really good mates. Probably cos she has an older brother, and also because she does girly girl (makeup/clothes/jewellery) and tomboy (football/rough and tumble) in equal measure. I don't think she sees them as any different. Although there is starting to be a difference between boys she likes and boys she "likes" IYSWIM!