This can be useful for others who have problems with search queries and refine the results by categorizing.
After your search query adds a space and a category name, and your search becomes more refined.
Here you will notice that only items in the Musician / Band category are returned:
http://graph.facebook.com/search?q=wilco%20musician/band&type=page
It works best when a category is a rather unique string. This particular search is not so flawless, but is still improving:
http://graph.facebook.com/search?q=audi%20automotive&type=page
Then you need to separate the other categories manually.
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