I agree with you about google's spell check, relevance, and speed.
DDG's !bang search is a killer feature for me, though. I can type "!wikipedia topic" in the omnibar and it gets me to the exact page I'm looking for, without stopping at a middleman. The same feature makes google maps, images, videos, and youtube easier to use to with ddg as my default search than with google as my default search. I have been surprised by the amount of search traffic that I redirect to something other than a general web search now that it is convenient for me to do so.