If you play World of Warcraft, you may have noticed that you might not have been able to log in to your server. This is due to the fact that Blizzard announced that they would be performing extended maintenance on a majority of servers to prepare them for the Cataclysm expansion, but it seems as though some of the realms have exceeded the scheduled down-time.
The planned maintenance times were supposed to be from June 8, 11PM PDT until June 9, 2AM PDT, but it has been some hours since this time frame was completed, and it seems that a vast amount of WoW players are still unable to log in to their server of choice.
If you would like to know which realms are still down, you can check the World of Warcraft Realm Status page to check which servers are currently still unavailable, and which are playable.
Which Realms are you having difficulty with? What time did you try logging on?