The new beta is no longer beta.. it was released on 5/13/08 :)
I should also note (becuase it seems that many are ignoring this fact) that type of portability and backup-ability requires named activation with an AdobeID (in Digital Editions 1.5).
If you choose not to use named activation, but rather to use 'anonymous activation' then you will not be able to backup and legitimately move your ebooks.
Regards,
Bentley Wolfe
Senior Support Engineer, Flash/Flash Player
Adobe