I don't understand why people think this is going to be useful. The inbuilt assumption is that people care enough about the data to want to search it frequentl

I don't understand why people think this is going to be useful. The inbuilt assumption is that people care enough about the data to want to search it frequently and thoroughly. I don't think that is true. Facebook is mostly ephemeral junk data that you don't care about; this has been true ever since they changed their UI to the Twitter-style "what are you thinking right now?" input / streaming. In order for search to be useful they first have to backtrack heavily on what their entire platform is about. Which would be hard.