One of our help articles ( http://help.duckduckgo.com/customer/portal/articles/216399-sources
) details our use of other sources and the 3rd paragraph goes into some detail about expenses associated with doing your own crawling. We believe that it is possible to provide great results without the need for user-data--which, on other engines, are mainly used for advertisements and result bubbling ( http://dontbubble.us/
When you say our results are inferior, it would really help if you could provide specific examples. That way, we can determine how best to tweak our internal algo and give you better results. Also, not every search consists of a user knowing what they want to find (specific webpage or document). In the cases where a user is exploring all possibilities (product reviews, research projects, general topic education), I'm not able to see any value in bubbling. Can you elaborate?