Do you think it differs here and there ?

when chinese call you a friend,that means you are a special person to them. we regard friend as relatives or more than that we tell each other about our secret when we are blue friends will be the remedy not just say hello it's a deep emotion in heart that's true friendship

Yeah as I said, I think you should ask fb and its Russian copycat users this question.

It's one of the most important things in Chinese culture, like God in Christian culture; even it's not so special now when some people say it. But it's more serious when people call you as "bro". In some place people even say: "bro is like body, wife is like cloth; you change your cloth when you want, but you won't cut your body". It's funny but I head this tradition makes western people feel there are too many homosexual people in China. LOL

The meaning of this word, its notion is the same throughout the world.