Arenanet has sent out emails to various players doing a survey on Edge of the Mists. Players can receive 400 gems for doing this survey. Check your email inbox to see if you were emailed.
Check your spam folder in addition to the inbox as Gmail tend to mark it as spam (Picture taken from Seiferian.6047)
The email title is Your Feedback is Valuable: Earn Gems and Help Shape Tyria!
From address is (email@example.com via firstname.lastname@example.org)
An Arenanet dev on the forums have confirmed that this email is indeed genuine.
This survey is coming from us. =D
Collect thy gems!
It appears only a small segment of the player population was selected
According to our marketing team, the e-mail went to a segment of players and was not intended for every player.
All the surveys have been distributed and if you did not receive such an e-mail in the last few days you were not in the current sampling and will not be receiving one this time around.