They got a huge boost out of the whole NSA fallout, which they consequently used to great effect for marketing. Good for them! I still hate the name, though.
I've been using DuckDuckGo as my primary search engine ever since the NSA fallout came, and the results are surprisingly usable for most common tasks. In some cases they feel better than Google because I'm seeing some useful sites that Google doesn't ordinarily show.
The only area where DuckDuckGo searches have been lacking for me is in finding useful technical articles and code results. Sometimes when I have to search for a complicated error message or research some programming problem to see how other people have approached it DDG will not work for me and I have to resort to Google or directly search Stackoverflow or something.
But it's already usable for the average person IMO.