Guild Wars 2 World vs. World matching system, and it's a subtle one that's almost invisible until you look closer. Because of the way ratings are calculated and how the matchups happen, the net result for each server is always being matched up against the same servers. No matter how well you perform, you wind up locked into a certain tier without any hope of changes. It's a problem that the development team is both aware of and is moving to address.
The short version of how things will work is that servers will be matched up semi-randomly, with ratings taken into account to assure that the spread between opponents isn't too severe. More math beneath the surface takes into account both the current rating of a given world and its overall deviation, producing a "real" rating that will facilitate fair matches. Take a look at the official blog for all the hard details.