Intimate Details

I was watching "Felicity" today and noticed how open all the characters are. Although I do realise that it's fiction, I can't help but think that there must be some truth in it. Fiction doesn't come from nowhere, there has to be some basis for it (in this case, the writers' experiences). Anyway, I was thinking if anyone does tell their friends every little intimate detail of their lives to their friends, and even acquaintances? What's your opinion on this? Do you think it's ok to tell people everything or should some things stay private?