I'm probably going to add some of my in-game friends as well since it will enable me to talk to them across alts, factions, servers, and other supported Blizzard games. I don't mean acquaintances, but people I've known for a long time and I consider them great internet friends. I value my privacy as well, but I don't think I'm giving away anything by having some of my in-game friends know one of my email accounts or my name. Their friends will only see my name, and that is probably the only part of it that I don't really like. However, it doesn't affect me enough to deter from the usefulness of the advantages of adding them as a friend to begin with.

Blizzard will probably improve upon it as they do most of their systems - especially considering this affects all of their games that support it.