Title says it all, expect something to come out of today. Possibly beta inivites, which are now automatically flagged in your account.
New ToS went live today didn't they? Its probably upgrades for RealID or something.
I hope it's the new battle net friends system.
I'm afraid it's not that special, just something is fucked up. If they were down in order to release the RealID stuff or something they would have mentioned it. No this downtime is definitely not planned I think.