I love Leighton, and Rowan as well!
I have only met 1 Rowan, (0 Leighton's) and he's 8.
However, the US and England+Wales stats for both are;
E+W: Leighton - 167th for boys, with 354 births, no data available for girls, meaning it ranked below the top 1000 with less than 36 births.
Rowan - 137th for boys, with 449 births, 573rd for girls, with 74 births.
USA: Leighton - 563rd for girls, and, recently fell out of the US top 1000 for boys, but had ranked 922nd in 2011
Rowan - 301st for boys, and 445th for girls.
So, going by the data, if you're in the USA, Leighton's gone for the girls, but isn't unheard of for a boy. If you're from the UK, Leighton's entirely team blue.
Rowan is a less obvious team blue choice, but it is definitely more popular for boys.
Personally, I prefer both for boys, and Rowena for a girl.
I know a guy in his late 20s with this name, even before Leighton Meester hit the scene I always thought his name was feminine due to it starting with Leigh-. though he pronounces it Lay-ton. (I dislike him strongly as a person so I never got around to actually judging this name as it will always be associated with him for me)
Well Rowan I was thinking was a girls name as I have only remembered ever heard it as a girls name recently, then I read lizben's comment about Mr. Bean aka Rowan Atkinson and yes it is definitely a male name. I'm not really into this boys name on girls trend but alot of these names I hadn't heard of/remembered hearing of so I automatically associate them with the ladies.