This whole article is predicated on "social search" being better than pagerank-scored search, which is only sometimes the case.

Sometimes I care what my friends think about a search query, e.g., "sushi restaurants near foo." It might help me to know that my friend Bob, who I trust, has been somewhere and thought it was good.

Sometimes I do not care at all what my friends think about a search query, e.g., "medulla oblongata." In fact, showing results that my friends might have liked in connection with that phrase may distract from the scientific information I am looking for, especially if they are pages of quotes from Fight Club.

Being able to distinguish this intent, and putting a good UX on top of it, is what Facebook needs to do to make a significant entry into the search market. (I'm not holding my breath.)