I have my accounts on 5 BNet accounts. I like using 1 auth code on all of them (at the same time). I also think or heard you can only have 8 accounts in 1 BNet account. So 5 WOWs, 1 Diablo III, 1 Starcraft 2 and maybe a couple older games (WC3, SC1, etc) and you are done. Then what put your Diablo and SC games on a different account, that kinda defeats the purpose of having one BNet account in the first place. I log into my account management about once every 6 months to a year.

I will want to move things between WOW games, so if they make things truely BNet account bound (probably not very soon, 2 years off), then I will probably just transfer the WOW accounts to one BNet. But to me that is a long way off and not a lot of BOA stuff is important to me to mail between chars.