As recently as 2 years ago while on a commercial flight I happen to glance out of the window and to my surprise a small private jet was headed directly towards our flight. I would estimate that the private jet was visible to me for perhaps 1 to 2 seconds. I assume what I experience is rare but I would have liked to have asks the pilots if they saw or where aware of the near air incident. I can only estimate the distance to be less then 1000 feet. This suggest to me that this shit is still a concern a real concern!