Cons of DuckDuckGo:
Because many of the places it links to are SSL, it's slower. Sometimes also loading DDG itself is slow, though it's definitely not like people are just sitting on their butts about this: a small dedicated group of developers are constantly trying out new things and improving old ones.
It finds less. Not much of a con though since you can get results through it from all the other search engines anyway.
For best results, make it the default search engine in your address bar.
This allows you to type the shortcuts directly into your search bar.
So I know I want a wikipedia page on Apple Computer:
!w Apple Computer
takes me to
I want whatever the first result would be for some given search (maybe I've searched it before and it's always the same?)
takes me to
It has partnerships with other sites, like Wolfram|Alpha for computational stuff (I type in !wa weather sliedrecht for current temps etc), Punchfork for recipes, tagdef if you want to search Twot hashtags (still haven't found what's useful about those tho), etc.
I like that if I type in something that does bring me to the duckduckgo page, I can keyboard navigate whatever... the zero-click info box is awesome (and often StackOverflow threads show up there... where instead of going to StackOverflow, I can hit the + sign at the top and just read the answer).
I like the little icons that show up on the right... it was strange how quickly I started relying on them to find sites fast.
You can either allow JS and cookies to set preferences, or just set them in the url as params instead.
And when I think it's not likely to have useful results (because let's say I'm searching something in Dutch which I expect google to have more of) I do !gnl (for google.nl) before my search. Google knows that DuckDuckGo typed in those search terms, but not that myIP/myBrowser/mySettings/myOS/myLocation did.