I really like it, boy or girl. I think it's a lovely name. I'd be more apt to use it on a boy, but most seem to be girls.I had the combo LarkinElisha for a boy. Loved it. :)
I like Larkin. It's one of the names that I am totally okay with on either gender, too. I currently have it fitting in a female combo.I like Lark as well, but Larkin better for some reason.
I encounter both girls and boys named Larkin here and there, so I'll comment on both genders. I think it's a decent name for a boy. For a girl, I prefer Lark.