Observer Mode

Observer Mode allows players of all levels and locations (out of Pre-searing) to watch the battles of the top 100 guilds in the ladder and can be reached by the pressing the B key in any town. The matches are delayed by 15 minutes to prevent cheating on the part of the participants of the battle.

One of the major benefits of Observer Mode is to discover the strategies that made the top guilds on top in the first place, whether it's a particular combination of builds or an excellent level of teamwork.

From the update notes (see the Wintersday Update):

That's right, Observer Mode!

Now you can watch as top-ranked guilds battle it out in the Tombs and in rated guild matches. The upcoming Guild Wars Regional Playoffs and World Championship will also be available for viewing as they happen. The details are as follows:

Whenever a top 100 ranked guild plays in the Tombs or in a rated guild challenge, the game is automatically available for everyone to see. Other "special event" games will also be available for viewing.

Everything that observers see is delayed 15 minutes from the original game, to prevent cheating. Games become available for observation approximately 15 minutes after they start, and remain available until approximately 15 minutes after they finish.

While you are watching a game, you can chat with your fellow observers. There is no limit to the number of people who can simultaneously observe a game, but for purposes of chatting, observers are randomly assigned into groups of about 100 people.

In Observer Mode, the Map Area window displays the positions of all characters on the map. You can click on any character to jump there. Alternately, you can use Auto Camera mode to let the game pick the most interesting targets for you.

A new heads-up display automatically shows you the Health of teams that you are currently watching. If you prefer to use the Party window to view party status details and to select players to watch, you can easily switch the Party window back and forth between teams, or you may choose to view multiple Party windows and watch different teams in each window.