This is a very valid and real concern considering there may be Facebook and other "social network" connections. Facebook is currently coming under fire for making marketing preferences (as AOL did years ago) and profile visibility/activity visible by default. When I joined Facebook I made everything in my profile except my name Friends only. After recently reading that they'd changed these things to open to the web, I went back and learned that not only was Name, Location, Age visible to web searches, but Friends of friends, and applications like Docs.com could pull all the other information out BY DEFAULT. It's a maze to try and go back and reset all of these things to the way they originally were.

It becomes more than a question of the security inherent in Real ID, but also that of the network they're connected to. Blizzard always suggests not to give your real email address out, but if another app or social network can pull that data automatically and that other app or network gets hacked....