Here’s a little tidbit from the latest info on Real ID:
Q: How does the friend finder in StarCraft II work? What’s sent to Facebook?
A: When you use the Add a Friend feature in StarCraft II, one of the options you’ll see is to search your Facebook friends list for people who also have Battle.net accounts in order to quickly send them Real ID friend requests. When you click this button, you’ll be asked to enter your Facebook login information, and you’ll then see a list of your Facebook friends who also have Battle.net accounts. You’ll then have the option to send any of these Facebook friends a Real ID friend request in-game. (Keep in mind that for someone to appear on the list, their Battle.net account email address must match their Facebook email address. In addition, you’ll see the names of any Facebook friends who have registered Battle.net accounts, regardless of whether they have Blizzard games attached to their account or just, for example, created the Battle.net account to make a purchase on the online Blizzard Store.)
It’s important to note that Blizzard Entertainment does not share any personal information with Facebook as part of this process. Keep in mind that as with other Real ID features such as the “friends of friends” list, our goal with the friend finder feature is to create convenient options to help players easily find people they know in real life on Battle.net without having to remember email addresses or account names. We hope players will find the feature easy to use and convenient.
So my facebook friends with battle.net accounts will be able to see if I also have a battle.net account? Hells no.
If you want to keep these spheres of your life separate, the obvious and quite easy solution is do not use the same e-mail address for facebook and battle.net.
As a side note, I’m sure the dude who doesn’t play Starcraft but bought something at the blizzard store for his nephew is going to be confused as shit when he walks into work and his coworkers whom he friended on facebook start yapping about how they sent him battle.net friend requests.