it's a no-no when you regift and the gift is just given for the sake of giving something (as opposed to giving nothing). to me, that's just fulfilling the basic obligatory requirement of giving something and is done mainly to absolve your own guilt over giving nothing.
if you've register but the gift truly suits the recipient then I see no issue. we ended up getting 2 copies of the same Jamie Oliver cookbook that we re gifted to someone who loves cooking and loves Jamie Oliver. I reckon it's ok in that instance.
as I said in the other thread, re gifting generic stuff like shortbreads or chocolates etc is also ok as these tend to have pretty mass appeal.
I've no issue with the idea of re gifting but it needs to be done in a considered and measured manner.
and never, ever regift anything used. that's just poor form.