In answer to some concerns about launch, Ferguson announced that the 24-hour match length that players are familiar with from the betas will be used until servers are consistently being matched properly. At that time, matches will move to the two-week format that WvW is meant to take.
In the same post, Ferguson listed the servers available for the final beta, which is noticeably shorter than the previous list. The world population limit has been "greatly increased," due both to the additional areas that will be open for player exploration and to some adjustment in how the team is handling its tech. Players should note that this is the initial list and the team is prepared to launch new worlds should the need arise.
Refer to the original blog post for the full world list.
[Update] ArenaNet has posted a few extra details on the official forums, world transfers will be free from the start of the beta until 9:00 p.m. EDT on July 21st. Gem cost for transfers after that time will be 1800 gems to transfer to a high-population world, 1000 gems to transfer to a medium-population world, and 500 gems for a low-population world.