In the past I would switch to it when I'm feeling some google-morning-after-shame (e.g. after seeing some targeted ads), I would stick with it for a day or two, but eventually go back to the 'what I wanted is on the first page' magic of google.
I've used DDG more consistently since changing the firefox search default, but there are still some things that I end up googling - sometimes DDG shows too many irrelevant results on the first page.
I think paying more attention to the bangs and moving away from 'keyword' searches will probably help - after all a tool is more useful if you learn how to use it properly - but for some topics (e.g. Haskell examples) if the first answer it finds isn't what I was looking for, the next couple of pages of results are usually useless too.