Petra - last I heard, even the European and Asian shards have to contact a login server in the states to log-in, that is separate from any of the actual shard servers (And only goes down once a week for maintenance). So anything that happens the the login server affects all persons trying to log into any shard, but doesn't affect anyone already logged in.
Granted, that's not to say that the log-in server failed ro reboot on its scheduled time, in which case there would be something to be worried about.
But, I've experienced inability to log in between 5:00 & 5:30-6:00 AM Eastern time nearly every week in September & October - it's just that there's a lot more people to complain about it because of people staying up late/logging in early for the events in the US, and playing around lunchtime in Europe. Remember, this is the first Tuesday after the DST switch in the US, and someone might have accidentally set the thing to reboot a half-hour BEFORE it went down, meaning that it would be down for a week, without intervention....
