I find it oddly satisfying to be able to use an app on my phone to identify planes above me. Do it all the time. I live across the Puget Sound from Seattle and I occasionally end up spotting a Boeing plane clearly on a test flight based on the route it has flown (geometric shapes, circles, take-off and return same airport).

Also had an interesting occurrence when I awoke to the sound of a plane dive-bombing my house. We happened to be located in an area designated to be sprayed for some sort of moth. The plane was just about scraping the tops of trees. But I was able to track and see the pattern it flew to spray our area and other areas it had visited that morning.