DuckDuckGo does not collect or share any personal information. Their privacy page has a great rundown on why privacy is important. The most important repercussion of this is that DDG doesn't use the data collected to tailor results, avoiding exposure to the "Filter Bubble".
For select queries DDG pops up a box that supplies the exact answer. For example, searching "stopwatch" will pop up a stopwatch, asking for "words like..." will show a list of related words, typing "password" will generate a password, etc.
Bangs are commands that allow searching via a different website's local search engine, using keywords or abbreviations with an exclamation mark (!). For example searching "world war ii !wiki" will automatically redirect to Wikipedia.org and show results for the query "world war ii" there, instead of DuckDuckGo, using Wikipedia's search engine.
The more common sites have shortened alternatives for these commands. Such as !g for Google, !i for images and !yt Youtube.
The whole list of bangs can be found by typing "!bang" in DuckDuckGo.
The ads are clearly labelled as ads and are non-obstructive. The ads are based on the searched keywords and there's no tracking involved on their visibility. You just need to remember that the site the ad links to might track you.
DDG allows customizing almost any aspect of the search engine's appearance including fonts, page width, alignment, header behavior, site icons, etc and has a selection of premade themes available as well.
DuckDuckGo has an API with some websites. With the help of this API, if you search for a fix of a problem in Linux, you can easily find an answer to the problem. For example, if you search for "How to update linux", you will get a message like this:
How to install updates via command line
sudo apt-get update # Fetches the list of available updates
sudo apt-get upgrade # Strictly upgrades the current packages
sudo apt-get dist-upgrade # Installs updates (new ones)
It's nice to adjust the settings and all but after a couple of days you will want to go back to a more functional search engine.
Sure DDG looks shiny and !bangs are great but many wouldn't consider it as a viable alternative. Better results for search queries is more important than fancy looking CSS.
WOT is a free, community-run website review system, to help protect against spam and malicious websites. Duckduckgo provides the option to display WOT icons next to website URLs, to indicate their ratings, without requiring additional addons to be installed.
Unlike Google, Startpage does not record user IP addresses and strips away any uniquely identifying user information before sending the search request to Google. For each search result, Startpage also provides users with the option of viewing them via Ixquick's proxy services known as Ixquick Proxy.
The optional proxy allows you to visit linked sites anonymously too. While in the protection of the StartPage proxy, the third-party sites and its advertisers cannot "see" you. Plus, the site cannot download malware onto your computer.
When you search using dogpile, it brings up content from many search engines to make sure you get what you're looking for. Some of the search engines it uses are Google, Ask, MSN, and Yahoo, and it aggregates content from all of them to display for you.
However DMOZ makes use of volunteers to oversee each category and if you have ever tried to submit something to DMOZ you will agree that the volunteers don't do much volunteer work. Therefore the system is very outdated and should be retired in my opinion.
Blekko believes by adding a layer of human curation on top of search results, quality can be improved. It makes sense, no algorithm can be 100% perfect on the near infinite breadth of search queries, so allowing people to curate the results to remove bad results and promote the best is a great solution. Blekko pulls searches from a list of over 3 billion trusted webpages.
Slashtags allow limiting the search to a set of trusted websites. Blekko has hundreds of slashtags across various categories that are all human curated. The Slashtags also help with discovering content in a particular category.
Blekko by default categorizes answers in boxes such as tech, social, or news making it easier to understand what's the context of the answers in each of the categories.
Additionally, the curation of websites and slashtags allow Blekko to provide context to results that may have multiple interpretations or when you want to find a particular type of information on a given query:
climate change /politics
climate change /liberal
climate change /conservative
climate change /science