We already know about the Blizzard Authenticator that'll be coming out soon enough. It is a little (optional) device that will act as a hardware based key which will be needed to log on to your account. This looks like the spot that you can associate one to your account with.
However the Beta Opt-In link is really interesting. This is just in time for all the activity at the World Wide Invitational 2008, and those of us at WoW Insider are speculating that all those beta keys people are getting at the WWI08 will be used there (there will be a goodie bag handed out to each attendee). However hopefully this will also let others get into the beta as well.
Right now the beta link points to the resurrect-a-friend program, and the authenticator link points to an un-published page - we'll let you know when they change over to a page with more useful information. Nonetheless, definitely something we all want to keep an eye on.