Safari lets you choose from three search engines: Google, Yahoo! and Bing. You may want to use a different search engine, and Matt Swain's AnySearch Safari plugin lets you do that. It can also turn off Safari's 6's "omnibar" so it doesn't search, and only functions as an address bar.
As a bonus, his KeySearch extension can expand the use of the omnibar to let you search on many sites, such as Wikipedia, Amazon, IMDb, and any site you wish to search, just by using keywords. For example, you can type "wiki Marcel Proust" to search for the Wikipedia page of that author.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20120806235032872