It was known to have just occurred in Cancer server and none of the players on other servers was affected. As Killerkev said, everyone lost guilds AND their friends lists (which is worse since many friends are on infrequently and they will not be able to contact them). The data was never restored (many were hopeful they would fix after next maintenance but it didn't happen), and seems like the response was "Here's extra 2xp but your friends and data and guilds are gone forever."