Source: [Only admins are allowed to see this link]
What's an overflow? Whenever you try to join a region such as Queensdale or Divinity's Reach, the Guild Wars 2 Network will try to locate you to your appropriate world, for example [Whiteside Ridge::Queensdale]. However, if [Whiteside Ridge::Queensdale] is full, you'll need to wait, since there are no resource left for you to play on your own world. While PvP regions will basically lock down and you'll have to queue up for them, in PvE there is a system called overflow. An overflow shard is simply a server which runs a copy of the instance you desire to visit. This will enable you to queue up for your original world's Queensdale, while still keep playing.
What's the problem of overflows? Many people actually get confused when they first visit an overflow shard. They aren't familiar with the system yet, so they might think that they are still on their home world, resulting in confusion when suddenly people start to speak in other languages (especially on EU servers). They might even confront them, telling them they should get off their precious world and go into their own, for examples if a player from [Abaddon's Mouth [DE]::Queensdale] gets on an overflow. Also it's sometimes hard to get on the same overflow if you try to group with other people, for example if player A is on [Queensdale::Overflow #1] and player B on [Queensdale::Overflow #3].
How can I check whether I'm on an overflow? Usually a message will appear when you enter the specific zone. If you happen to miss the message, you can just check your minimap. It will show your current region's name and "Overflow" if you're in an overflow.
What should I do when I'm on an overflow? Just continue playing. If you try to group with other players in the same overflow, it should work without problems. If other players join in later, they should get automatically moved to your overflow if they weren't in the zone before they joined the group. Otherwise they can click on your icon and use "Join in" to actually join your overflow shard (notice that this was broken in both the last stress test and the first hours of the headstart, I guess this has to do with authentification aka login issues).
If you encounter someone who doesn't seem to understand the overflow system, looks for guild member, or is agressive about people speaking English, explain them the system. It's one thing to hate someone for his actions, but a greater deed to tutor someone into a happier experience.
How long do I have to stay on an overflow? That depends completely on your world's region's load. It can take up to one hour, or end instantly. This is why you should try to gain a friendly atmosphere on an overflow shard, as you may be stuck for another hour with these people.
Don't forget, the more you know, the more you can teach, the more you'll help. Hopefully this helps some people to handle overflow situations. See you all in game, when the log in servers are ready again.
