Yes, I know people have rasied this issue before*, but I'd like to do so in a much more aggressive way.
If DDG wants to make a splash (pun intended) in the search engine space, the single most important feature DDG should implement is a client-side ability to tell the DDG search engine which sites to continually omit from search results.
Between SEO-driven keyword pollution and content-farm pollution and pollution created by affiliate marketing on sites like Amazon it's almost impossible to conduct clean searches any more. Much worse, however, is the fact that I know in advance that I do not want any search returns, ever, from many sites that rank highly because of SEO abuse, yet even on the cutting edge of computer use the option to exclude known search carcinogens is unavailable to me. (I believe Google does offer something along these lines, but not surprisingly it's only for people who stay logged in.) How is it even possible that this is not a normal function in almost every search engine? (The que$tion obviou$ly an$wer$ it$elf.)
The advantages of allowing me to omit any search returns from Wikihow or most of the 'Answers" sites is that I get better search results, which is what you want me to get from your search engine. This may not be what Google wants because it hurts their own money-grubbing business, but DDG doesn't seem to be in the advertising business so why not offer this to users? It's a KILLER APP in the search market.
Give me the individual ability to black-list sites and over time I'm going to auto-improve my own search returns more than you will ever be able to do for me. I know I don't ever want to hear from various news sites, various how-to sites and various marketing sites. I will never value them as a reference or trust their content, yet I still have to sift through that drivel in order to find hits that are of genuine interest.
Do this. Put it on the front burner, roll it out, have people give you feedback and make this work. You will not believe how much press it gets you and how quickly many nefarious content providers will start squealing. There's no excuse for not making this happen. Hell, there's no excuse for not making this the central feature of DDG that distinguishes it from all other search -- along with your we-don't-track-you ethic.