I have a couple concerns I'd like to share:
First, duck.co seems to leave a tracking cookie behind, I'm not sure why. Could it just be the software you're using (I remember something like that in the past).
Second is Bing ads. I understand why you can't just use your own ad system. However, when you click on a Bing ad, it redirects through MSN so that DDG can be payed it's share (and so the advertiser can be charged). Unfortunatly Microsoft does not have the same look on privacy and one can be certain that one is being tracked through that.