My wife and I recently went to see the movie adaptation of the Christopher Priest novel, "The Prestige". We both enjoyed it. Afterwards a certain similarity in a plot twist in the movie jumped out at me (like as soon as I hit the lobby) to a piece of business in a well-known story by James Patrick Kelly. I won't divulge it in case you haven't seen the movie. I e-mailed the esteemed Mr. Kelly and asked him about it.
As it so happened, he went to see the movie with his wife the same day, and yes, he knew what I was talking about. He said (tongue in cheek) he would have sent his crack legal team after Priest except both his story and Priest's book came out at the same time (which is true - it was 1995) and so there was no way one author could have known what the other was writing
It was a very pleasant exchange. And it leaves me wondering, why does this happen - different people all come up with the same idea at the same time? You hear editors mention it all the time.