That's pretty cool. I get all geeky about this stuff.
Just to clarify some info in the article:
The sound barrier is different depending on altitude. At sea level Mach 1 is 761.2 mph. Where as at 36,000 feet its 654.6 mph because the air is thinner, and thus less resistance.
So the Mach 1 of 768 mph is the speed at ground level. An airplane at Mach 1 would actually be going slower.