I have had my 1DX since Nov 2012. Other than having it serviced for the technical advisory (recall) for lubrication check, and a clean and check last Feb, it has served me well. I have experienced a couple of things with it that never occurred with any of my other bodies. I was shooting the mission in San Diego, when I had a blank image occur in the middle of a series of shots I was taking of some of the art work there. I took the shot and looked at the LCD, only to see an all black image? This has only happened once with my 1DX, but still puzzles me! The blank image contained all of the right exposure information, just like it would with a properly exposed image, but no image was recorded? I checked the System Status Display and found an error 80 code. However, upon checking the event time, it was for several days prior to the blank image and when I checked the time code against the shots I had taken, there was no problem with the images shot before the time code or after it? The only other issue I have had, is that both the original battery (LP-E4N) and one of the extra batteries I have for my 1D4 (LP-E4) display the "Recalibration is Needed" after about six rechargings? Performing a recalibration did not clear this issue with either battery? The original battery for the 1D4 has been recharged at least a dozen time without this ever happening? So, other than those two issues, it has been a complete delight using the 1DX!
UPDATE: Just tried a method of recalibration suggested by a friend. Charging the batterys fully before attempting the recalibration, did the trick! Although it takes about 14-hours to complete this process, it cleared the "Recalibration" message from the battery status display.