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".
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 i...
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.
DuckDuckGo is a great alternative to Google. I love that it values user privacy and offers great functionality. Granted, sometimes Google gives out better results, but for the vast majority of queries, DDG is virtually as good as Google.
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 P...
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 Therefore the system is very outdated and should be retired in my opinion.