I think
Deborah is a GREAT name (and definitely the way to spell it if you don't want it to look/sound like you're advertising a bra size) and not overused at the moment... have met just a few around my age, but most are older... except for a friend of mine's daughter who is 9 now (when did she get that old?)... for nn.s,
Deb is definitely preferable to
Debbie (if one must go by that nn, I think
Debi's a nicer spelling) unless you're in Jpn. and they add vowels to the end of everything and it would turn into debu (fat).
Debbie kind of has 2 images... rather conservative style bank teller/business woman or beach bimbo/airhead. I know there are Debbies that don't fit that description, but I'm still not a fan of the nn.