As much as I love DDG, I personally find it a hard pill to swallow knowing that it's not truly an independent search engine and just an API relay of Google's stuff. I do take comfort that Google isn't getting data from 90% of my online searches, but it would be awesome to know that DDG was truly its own entity and won't be cut off for some reason in the future, like we've seen with Scroogle (which, I believe, was mostly due to API changes, not ToS violations).
Even if DuckDuckGo did get blocked eventually, it could easily switch to using a separate service. If Bing ever blocked it off, the code could be slightly altered to use Google instead.