I find myself using it a lot for things like seeing "Sergius, Abbot of Holy Trinity, Moscow" in the Book of Common Prayer and thinking "Huh, who was he, I wonder?" Select, Left click -> Search (Books)
Most of the time, I get a synopsis, taken from a bunch of my books, which I really appreciate for an overview, which is all I'm looking for anyway.
Today though, I really appreciated this, believe it or not: the synopsis essentially told me when he lived and when his day is celebrated but then acknowledged that there was no other biographical information available on him where it searched. Ok, thanks for letting me know! And then just to make sure, I had it search "All", where it found results in books I don't own. Fair enough.
Anyone else finding themselves thinking, "Say, this could come in handy!" (even with the proviso of checking results)?