Under Settings - Privacy, DDG offers
Address Bar - Hide Query
Whether search queries will appear in your address bar (GET vs POST requests).
POST queries are an important privacy enabler because UK law demands that ISPs keep a record of the URLs that people visit. Any search query typed into ddg and fetched using GET is permanently logged and can be searched by police and security services by negotiating with the ISP, without letting the user know.
When the search term is transferred using POST over https, the ISP has no access to the search term - they can't read it without cracking the https - so the search term remains private. So hiding the search term from the address bar is a major privacy enhancement, in the UK at least.
Unfortunately, DDG gives the game away. I used Chrome - view - developer tools - network to look at the network traffic when I typed "hello" into the ddg home page. DDG does indeed send the query over POST.
However, before that, DDG sends data with every keystroke, with a GET:
And that callback=jQuery110209023988840635866_1400658636352&q=hello contains the search term and must by law be retained by the ISP and must be provided to authorities on legal request.
At the very least, DDG should point out that the hide-request feature does not provide secure searches. Preferably, all data, including individual keystrokes, should be sent by POST, not GET.