After doing my first Deja Dup backup to my Ubuntu One service I noticed the folder show up in the list of folders to sync with my device. Should I sync this folder, why and/or why not?
I would advise against it. Depending on your settings in U1 and Deja Dup, this could end up turning into a recursive backup situation, where your next backup contains a backup of your backup directory, etc. etc. Seems like a good way to eat up all your disk space on U1 though :)