But that'll change soon.
Those who have the beta enabled on their account can copy characters to the beta servers. Remember to check out the Beta Opt-In Info and FAQ if you've got questions about the process.
Looks like it could be an exciting night!
Update 8:45 p.m: Here are the available servers for people to copy characters to.
Update 9:01 p.m.: New install screenshot, we now have ... a button! Which still doesn't work.
Update 10:00 p.m.: Mac users are able to download the beta, no such luck for Windows folks.