Heads up :
Do I need to sign an NDA to participate in a Guild Wars 2 Beta Event?
Yes. All participants are required to sign an NDA. All content in the Guild Wars 2 Beta Events is confidential. If you are participating in a Guild Wars 2 Beta Event, you should also not disclose that you are a participant.
What does NDA stand for and what does that mean for me?
NDA stands for Non-Disclosure Agreement. An NDA is a legal contract between ArenaNet and you that states all content in the Guild Wars 2 Beta Events is confidential. By signing the NDA, you agree to not disclose that you are a participant in a Guild Wars 2 Beta Event and to not disclose any information about the content. Breaking the NDA can lead to legal proceedings.
What happens if I talk to my friends or the public about being in a Beta Event or post screen shots to Facebook/my blog/my fansite?
By signing the NDA you are entering into a legally binding contract with ArenaNet. Any "leaking" of information, images, or your participation in a Beta Event will result in serious ramification, up to and including being barred from participating in future Beta Events with ArenaNet, account termination, and legal proceedings.
Why do I have to sign an NDA?
ArenaNet has a right to protect its intellectual property. You are entering into a game world that is not complete and that is still in the testing phase. Any information or images released at this stage may give an incorrect representation of the game or unveil confidential information that jeopardizes future development.
Source:http://www.guildwars2.com/en/the-game/game-faq/#seventeen