I know this thread's a bit old, but I thought I'd add our story.
I'm one of those Moms who enjoy doing their son's hair in curls and 'girly' styles. He's had long hair all his life and a few years ago he asked if he could have curls, like his big sister. After some hesitation I took him to my stylist and she did some curls with a curling iron -- he loved it and I could not believe how pretty he looked! She suggested I try some rollers at home so I did him in my hot rollers. Since then (He's now 10) I've been doing his hair on rollers a few times a week and I take him to the salon for a trim and roller set once a month or so. I've gradually added headbands, barrettes, etc. He'll even sleep in foam curlers on Saturday night before church!
For school he wears a high ponytail, or a headband, or braided pigtails. My stylist says she does probably one or 2 boys a month in girls hairstyles, brought in by their mothers. She has a couple of 'regulars' and she thinks it's becoming more common.
I think the difference here is my son actually asked to start curling his hair. He loves his hairdos & I think it's fine to let boys express their girlish side as long as it's their choice.