Urban legend or not it's a great lesson. My niece has a blog and about three months ago she got a new cellphone and plastered the new number all over her blog! I couldn't believe it. Her name, age, birthdate, city, and now phone number where all over the blogsite. I called her and screamed at her then yelled at her dad.
Also, a friend of mine wrote a fictional novel that deals with this very thing!!
http://www.lulu.com/vferrari
buy it, read it, and if you so choose, give it to someone you know (i.e. your young teenage kids) to read as well!