To be honest this is blizzards best but worest id ever doen, you will see the email addy for anyone u realid friend and all there friends can see your addy. I am sorry butt his is a keylogger dream if they can hack you, they get all your friends email addy's and they can spam them. personally I think that this iis may sound nice but once one friend gets hacked the keyloggers are in. if I friend one person any of their friends see my email and my firneds, so it will be a dream world I personally do not recommand this to anyone. here are the faq's about it
http://us.battle.net/realid/faq.html
http://us.battle.net/realid/faq.html