I learned a long time ago, the hard way, never to put complete trust in anybody. There are things that I would never even consider telling anybody. I know one or two people who I have been friends with for years and would, if absolutely necessary, trust with something important to me. But I wouldn't go telling them these things for no reason.
On the other hand, I don't act all cold and nasty to people I hardly know/don't trust... I'm just selective with what I tell people.