I'm torn. On one side I really like it, it reminds me of the old People Search feature Facebook used to have. On the other side for third party developers especially those who try to make the Facebook experience better, I'm afraid this is reinforcing the point you should not build 100% on platforms.

I'm sure there are many who have had this idea or are building this currently. Facebook Heroku templates given for new developers to start with, hit on the four main areas that Graph Search seem to provide.

Another example would be a query like

    movies liked by people who like movies I like

In FQL the closest I would have gotten was

   SELECT name, page_id from page where page_id in (SELECT page_id from page_fan where uid in (SELECT uid2 FROM friend WHERE uid1 = me()) and profile_section='movies')

And even then FQL was unstable

So then you wonder, why use an app with an unstable query built on an API filled with bugs when I can faster get the result using facebook.com?