I noticed myself as a user who likes the privacy-idea of DuckDuckGo, that what have keept me from using it in every day, is that the domain http://duckduckgo.com
is too long and complicated to type.
That sounds like a small thing, but when you want to search for something quickly this small things matters
I think what you should do to make this search engine more popular is always using a shorter domain by default, like duck.go (which you already own)
When people go to duckduckgo.com it should work, but it should redirect the URL to duck.co to make it clear you don't have to type more then that
I think this change could have huge impact in the spread use of DDG. I deeply about privacy so that is why I want you to give it a try