ArenaNet has announced via Facebook it will hold a stress test for Guild Wars 2 tomorrow from 3.00pm - 7.00pm EDT.
This explains the client update from yesterday.
"Unlike previous stress tests, we will be actively working on the game during the event, so you might experience connectivity problems or discover features that are not working as designed," reads the developer statement. "Any issues you experience are a result of the rigorous conditions of the stress test, and are in no way representative of the state of the game at launch.
"By participating in this stress test, you’re helping us make Guild Wars 2 a better game."
Guild Wars 2 launches August 28. The countdown starts.