In an effort to stave off diminishing populations on their many, many servers, Bioware are in the process of moving all their players on to a few mega servers. This both sounds cool and is cool. A combination that is rarer than it sounds.
Earlier today Bioware switched on their public testing server, and created duplicates of all the characters across the servers housing players from the American Eastern seaboard. Any of those lucky lot can hop into the test server and see what it's like to be on a server many times largely than the standard fare.
It's very much a beta period at the moment, and players are encouraged to report bugs on the forums.
Just in case there's any confusion this public test server is separate from the one currently running the 1.4 update.