I think it differs from personality... my best friend -which is a girl- and I are really comfortable around eachother.. we love to hold hands, hugging and just doing some weird stuff I'd never feel comfortable doing with a guy.
However I do have a couple guy friends whom I'm very close to spiritually and emotionally. And yeah, since I've tried the 'dating your best friend'-thing eith my best guy friend and that ended up in shatters, I've discovered that I crush on people I dont know, and once they become good friends, i cant imagine why I crushed on them!
It sounds horrible but its true unfortunately for me.