My phone number and home address are secret except to family and close friends IRL. Everybody else can use email and the PO Box. :-) People can be wildly different online and face to face. Usually they are horrible online and lovely IRL, but sometimes it's the other way around!

I've experienced some minor cyberstalking. A warning (like "Do not contact me again. I'll report your next email to your ISP") has sometimes been all that was needed. When ignoring them, or warning them, hasn't done the trick, making a hell of a fuss has helped: publicly posting one harasser's emails in Usenet stopped her, complaints have stopped others. Realising that their actions are not a game and have real consequences seems to make them stop and think.