Tuesday is Server Maintenance day for World Of Warcraft. Always has been, always will be, so please don't freak out!
Every single Tuesday, from the very beginning of (WoW)time until the very end of the World(of Warcraft) is set aside for Blizzard Network Engineers to maintain the game servers in order to provide 11 million players with the best gaming experience possible. This is no easy task by any stretch of the imagination, with more than 250 individual game servers to work on and only a few short hours to do it in, even something as simple as rebooting the servers can take several hours to complete. Blizzard ALWAYS puts a notice on the game login screen before maintenance happens to give all players an idea as to the nature of it. This will be in a message box located on the left side of the game login screen, where you type your password.
Typically, most Tuesdays are simple server restarts which usually means each individual server is only offline for about 15 minutes or so at most, but the whole process can take an hour to complete for all servers.
Sometimes the server will need more maintenance than that, maybe a cooling system failed, perhaps a hard drive died, or something needs replacing. These Types of maintenance can take several hours to complete, but typically only affect the population of that server directly, and maybe, depending on the scope of the problem, could cause other servers within the same cluster to have connection issues. These problems are extremely rare.
Other times the server maintenance has more to do with the actual game files than anything else, many times this involves applying a new patch to the game. Maybe they need to fix a problem with a dungeon, fix a graphical glitch, or maybe change the way some spells work. There could be a content patch that changes game mechanics, adds new dungeons/armor/monsters/spells/etc. Software changes will affect all servers, so they must be applied to, installed and tested on each server to be sure the patches were successful before the server can come back online for play.
Sometimes this goes smoothly, but not always, sometimes there's issues and further patching needs to be applied to fix the problems. These types of maintenance can range anywhere from about 1-6+ or more hours, and if there are seriously major problems a server could be offline for a day or two.....however these cases are exceedingly rare, and Blizzard almost always adds free game time to players accounts to compensate for the lost time during maintenance.
This compensation can be seen by logging into your battle.net account, under the "Your Game Accounts" section click on the World of Warcraft game. Now you should be at the "Game Management" page for World of Warcraft, to the right of the picture of the game box, click the "View Account History" link.
Play time compensation will show up in the list of payments and look similar to this; "9/18/09 N/A Three Day Credit Expired". The Date is the date the credit was given, the "N/A" is under the "Amount" column (meaning there is no cost), Then the amount of time credited to the account, followed by the status of the credit. The status shows as "Pending" when the time is first credited to the account, and it shows as "Expired" when the credited time is used up.
So, as with every Tuesday, there's no need for anyone to freak out. All of your characters are fine, your computer isn't broken, and your internet connection is fine. The game server is just offline to "get the oil changed" and will be back shortly. Go out and enjoy the weather, play fetch with your dog, go play with the kids toys, ride a bike or take a walk!
Thank you for your attention
Defender of the New Player Help and Guides Forum