Every browser searches from the address bar now - Opera, Firefox, Chrome and new Safari. It would seem then that Apple is implementing an option that is now, for all intents and purposes, standard browser functionality.
Honestly, there's little that makes it magnitudes better than two separate fields except for one small thing that, for me at least, becomes habitual: using one field makes it easier to search through content and go to URLs because I only need to worry about one keyboard shortcut to give it focus (Command+L). Having used combined address/search bars for so long, I can't tell you how often I would open a browser (Safari) with two fields and frequently put the wrong content in the wrong field.
Thus, I'm willing to bet that although the advantages may seem negligible, they become habitual (like much else) and two field browsers will seem counterintuitive once this is so.
