It's amazing how close those jets appear some times.
I remember last summer I was on a 737 headed for Las Vegas and was staring out the window... and to my amazement another 737 went ZOOMING by!! It was close enough to see it see that it was the one of Alaska Airlines new 737's with the winglets. Even that jirk in the back picking his nose.
Anyway, that was my first experience with RVSM here in the States. lol :p It was pretty sweet too!
Reminds me of my last commercial flight (first leg)... I was leaving Vegas, bound for exotic Colombus, Ohio, and somewhere over Iowa I think, in the first faint light of dawn, I saw another airliner converging from the left ... wasn't 100% sure it would miss until it had almost passed overhead, at which point it looked to be at least 1000 feet above. A little unnerving...
First time I'd seen that, although more than once I'd caught a glimpse of another jet at the same FL going in the opposite direction- really drives home just how fast you're going... :o !