I believe you have to earn the trust of a child and go on example for the trust to grow
we are very hot in this house on privacy. I would never and have never looked in diaries or mobile phones and I too would be horrified if my kids read mine (I have a house of teens)
My sister can't believe I don't give my teen daughters a time to come home at night, I have never needed to. They understand that after 11 I deserve a call and an update. My niece on other hand has curfews and is late and gets in trouble. It's a vicious circle
If a youngster trusts you, they will confide
I know that my kids have tried smoking, my bigger girls have confided how far they have got sexually and are happy to ask me advice on all subjects. I am not a friend to my children, I am a parent and their are rules (when one of my sons wasn't where he said he'd be recently, he got a rollicking and consequences) I just choose my battles
I think trust is something that should be started from a young age and even young children need a safe space like a diary, to put there thoughts and help them work them out
The computer stuff is slightly different. I don't read their conversations but do check on what websites they have been on. The msn society we have today just replaces kids being out playing with friends (the good days lol) It does pose a problem to being more anonymous and does make it easier to say things you wouldn't say in RL.
Hopefully, if people have a relationship that is secure, children will come and ask questions or be secure enough to tell someone off if they offend
Technology definitely makes parenting harder though