Yes, they ARE shockwaves!
More than 20 years ago, I have been lucky enough to see shockwaves from an ideal position. It was during a DC-10 post-Heavy Maintenance test flight.
With the sun to our left, I was kneeling near one of the many shiny polished cabin windows, say near the inboard wing trailing edge. This was in an empty convertible freighter cabin: no seats in the way and choice of all windows. On the RH wing, I suddenly noticed something resembling the shadow of an 8 feet tall whip antenna (like you see on old army vehicles). I was fully aware that our faithful Tri-Jets don’t have anything like that, and ‘on top of that’ the shadow moved slightly forward and aft all the time, as if it was an antenna with the base moving forward and aft on some rail on the fuselage crown. I also remember it was noticeably less sharp than the shadow of the fuselage itself!
The test team confirmed that this visual effect could only be caused by shockwaves; they were just verifying the airframe behaviour at high Mach number and the MMO warning.
The sun was indeed roughly in the plane of the front spar of the RH wing, so several members of the team then took up positions slightly aft of the front spar where we had an excellent view of the sort of wrinkled glassy transparant curtain that kept wandering slightly forward and aft chordwise, but always close to just aft of the front spar.
The tell-tale ‘shadow’ I mentioned was caused by slight refraction of the sun’s rays almost in the shockwave plane separating colder and slightly warmer air!
Without the choice of windows, but luckily strapped-in just aft of the front spar, I have since seen these shockwaves also in an IL-62. The visual discontinuities moved and became more noticeable during turns, particularly against the background of the ground when “my” wingtip came down.
I have complete understanding for those who think to see something else, or even nothing at all, but trust me: these look fully like shockwaves (and can hardly be something else).
Shocking but true. 
Plumb Bob
Last edited by Plumb Bob; 10th Jan 2007 at 05:40.
Reason: ‘slight reflection’ corrected into ‘slight refraction’