EDIT: Ooops, this is just for international countries who have had their Nationals. This does not apply to the United States yet. The United States’ invitations will be sent out after Nationals.
The Worlds 2008 invitation e-mails have been sent out for some international countries. If your Pokemon Organized Play ranking is high enough, you may have been invited to attend. Here is the beginning of the e-mail, thanks to Jasemew:
Dear POP member,
You are receiving this email because we have pulled the final results from your ratings zone. We are pleased to inform you that you have earned an invitation to participate in the 2008 Pokémon TCG World Championships in Orlando, Florida from August 15th through August 17th 2008.
If you do not have an invitation to play in the main Worlds tournament, you can still receive one by making it through the Grinder tournament held at Worlds one day before its main events. More information on these events can be found at the official Pokemon Organized Play website.