Dang it! I just bought a 1DsMkII from a guy here on the B&S board and have noticed this on some of my high shutter speed images. Didn't know what it was. Now I do and I'm not real happy! He said it was just back from Canon with a clean bill of health, but didn't produce the receipt. Only has about 25000 clicks on it, too. Sucks!
Well... I don't know if their prices went up or something but I got quoted $279 for service + $142.35 in parts. Sheesh. It was at 65K shutter counts. I kicked up a little stink and they gave me 20% off but still...
Had the same issue shooting anything over 1/500 sec. on a 1DS MkII and it cost $146 total back in Mar 2012 - Gold membership discount - the shutter unit was free and only paid for labor!