SafariKeywords teaches Safari a feature that's long been available in other browsers, such as Mozilla or OmniWeb and is known as "Mozilla Keywords". It basically lets you tell Safari where to search for the words you entered into the search bar, instead of always consulting good old Google. If the first word of what you entered is the name of a shortcut you defined (or one of the factory defaults) in the preference pane, Safari uses that shortcut's URL instead of Google. If not, it defaults to Google.
What's new in SafariKeywords
Now uses custom default search engine, if configured