We have another developer’s blog givings the rules of switching worlds, and how the whole system works. Players will be able to play and transfer to different servers at will. While all players will have a “home world”, you will be able to guest on any server that you want to play with friends. Server transfers are available once a week for a fee.
While you can change your home world, there is a limit of one world transfer every seven days per account and a charge of 1,800 gems for each transfer. A world transfer moves all of your existing characters to your new home world. Any subsequent characters you create will also play in this new home world.
When Guild Wars 2 launches, you will also have the option to play with your friends on another world with our free “guesting” feature. With guesting, your characters can play on any world where you have friends—with certain restrictions. For instance, you will not be able to participate in WvW while guesting.
While home-world selection and world transfers will be available during our Beta Weekend Event, guesting is not currently available. All players will be able to receive 2,000 gems free for the Beta Weekend Event, so you will be able to purchase a world transfer if you find yourself in need of one. Since the limit is one transfer every seven days, you’ll only be able to change worlds once during the Beta Weekend Event.
Source: Choosing and Transferring Worlds in Guild Wars 2
Keep reading for a list of the servers for this weekend’s Beta Test Event.