I was in the back of an A319 flying up to Edinburgh last week. In the cruise a 737 slid over the top of us, maybe 20 degrees heading difference. My instant reaction was "bloody hell, he's close", but with a second look it was obvious that he was certainly 2000' higher and very likely more.
I suspect that the 737's vapour trail gave an illusion of nearness - I don't believe I've ever seen another trail quite as close as that before (I don't fly as often as I would wish!), therefore I am rather more used to seeing them from the ground than regularly from the air.
Incidentally, I can't think of any mid-air collisions out over the North Atlantic in recent memory. I seem to recall something like a DC-6 and a Connie collided off the west coast of Ireland in the 1950s?
My only worry mid-Atlantic is whether there will be any turbulence severe enough to stop lunch/dinner being served!
