If you use Firefox, and you Shift-Return a search in the Google search box, Firefox will perform an "I'm Feeling Lucky" search and show you the corresponding page. However this is not the case with Safari, but you can get a similar result using the free Safari plug-in Safari Stand's Quick Search feature.
In the SafariStand settings, enable Quick Search and add a new line called something like Google lucky. Set a shortcut (I use l) and define the URL as:
http://www.google.com/search?q=@key&btnI=I'm+Feeling+Lucky
You can now perform a Google "I'm feeling lucky" search directly in the URL address bar by typing something like l osxhints. When you press Return, Safari will open up the first match from Google.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080725175953832