Ok, I know it is insane but I saw "something" 2 years ago when I was out in the yard.  Middle of the day even.  I was filling up baby pools for the geese when I noticed they all had their heads turned sideways to look at something in the sky.  They used to do this often when they were smaller because we are under a flight path to the airport, so planes go by often.
So anyway, I look up to find the plane but instead I see two grayish boomerrang type things doing this kind of weaving in and out dance in the sky.  They were small and at first I dismissed them as birds.
Just as I came to that conclusion a plane flew by....only it was 
below the boomerrangs.  That plane was pretty high up - not like it was going in for a landing, it was high.  So then I was confused, yet still those boomerrangs were there doing their weaving in and out thing.  I watched for several minutes trying to make sense of it and then they were gone.
I don't know of any bird that flies at that altitude and could be picked out of the sky from earth, but if anyone else does I'd love to hear it. 
  If they were lower and that plane had not flown past to give me a size and altitude comparison by I would say they looked like extreme hang glider guys doing some sort of show.