Facebook's GraphSearch has been, in a word, abysmal. The results are irrelevant or non-existent and, even worse, they can't find basic Facebook-specific content which forces you to Google it and then click back to find Facebook content.
But, GraphSearch launched not too long ago -- so why the change? Even with its poor performance, it must have turned people off -- or worse, they're flat out not using it. Today Facebook changed the search box to be a more prominent white instead of the blue bar that used to sit at the top of your browser. See for yourself here:
Will it pay off? Does it matter? Honestly it doesn't. Facebook won't win in search, and GraphSearch will eventually land in a long list of me-too products that the company felt okay throwing in to the scrap heap.