Arenanet has announced that the Megaserver technology has been fully implemented in all PvE maps and Heart of the Mists.
Although we’re excited that you have more players than ever to explore the open world of Guild Wars 2 with, our work is not yet complete. Our megaserver team will continue to monitor the performance of the technology on live and evaluate your feedback. We will continue to tweak and update the way the system works until it is providing even better megaservice!
(Source: Guild Wars 2)
MMO Fallout 