Martin Kerstein has written and published a new blog post tonight, this time on world selection, the cost of world transfers and what "guesting" means to those that want to play with their friends across worlds. When you first launch and login to Guild Wars 2, you will be greeted by a selection of servers, or as ArenaNet has termed them - worlds. You can choose any server you like, even those outside of your region (though "to select a home world that is in a different region from where you purchased your game, you will be logged out for a short period of time while your account is moved to your new region"), but note that this will become your world server and you won't be able to switch unless you're willing to pay for a world transfer with 1,800 gems. However, once the game launches, you will be able to play with your friends on other servers with the "guesting" option - you can play with them as you please with a few restrictions, one being that you can't participate in WvW.
While you won't be able to use the guesting feature this weekend, all participants will be able to receive 2,000 gems to help facilitate transfers. With that being said, it's probably best that you make plans with your friends and guild before the BWE launches this Friday.
It was also announced earlier this evening that the forums are up for the community to download the Guild Wars 2 client. By the looks of the @GuildWars2 Twitter account, it seems they are having a few hiccups so if you aren't able to view the forums now, keep trying!
For more information about the upcoming Beta Weekend Event and other Guild Wars 2-related info, make sure to check out Guild Wars 2 Guru!