it was playing up yesterday as well. i had just got my 24 shammy into a group to run RFK and we all lagged out and couldn't sign in for maybe over an hour. later on you could tell something was up because Orgrimmar was empty, there were like, 3 people there, and at that time of evening? it was a bit surreal.
and the server is down again today. something to do with the Cyclone battlegroup.
i am hoping it will be back up again when i get in from work this evening (at abut 10:00pm btw any guildies who read this :) ).