I have graph search enabled on my account now, and it's terrible for anything beyond photos.
Honestly, I think that Facebook's biggest problem right now is dirty data. They have great, personalized information on millions of people. But they also have tons of shit accounts created to game their system. Before their "graph" maps in any real way to their flesh-and-blood users, they're going to have to clean house big-time.
If they can actually accomplish that, then graph search will give them the one piece of marketing intel they don't have right now: instantaneous consumer intent, ie what their users want right now, not just what they're interested in generally.