I'm running DOpus from my USB drive. The backup and Restore option in the menu is greyed out. is this on purpose?
I don't know the reasoning behind it working that way but since all the config is stored in files you can simply copy them to do a backup.
(They can also be copied to a HDD install if you want, just make sure you copy the settings folders to the appropriate places (see the FAQ on config backups) as HDD installs have three settings folders while USB installs keep everything in one place.)