Short answer: I open up to everyone who is interested. I'm comfortable with sharing almost everything (except my PIN number), but it can't be a one way street. If you want to hear the stupidest thing I've ever done, you better be prepared to tell me your craziest move also.
How do you know who to tell what? Just follow your instinct! If the conversation flows from the mundane to more personal stuff and it feels alright to share, share. If it doesn't feel right, change the subject! Works for me
Jim.