The new (version 2.0.3) Preference Manager backup tool from Digital Rebellion stores it's Final Cut backups as .pmb2 files which are simply "Directory" according to the File command. What this means is that you can access the files backed up simply by right-clicking on a .pmb2 file and selecting Show Package Contents.
I'm unsure how well these backups will transfer over email or via Windows systems, though.
One more quick note: if you try and use a / (slash) in a backup's name Preference Manger will not create a backup and not warn about it since / is an illegal character in OS X's file naming system.
For info about the old file format look here. Apparently your old backups are converted to the new package type automatically when you run the app for the first time.