Have my 1Dx now for a couple of months. Send it twice to a Canon service center for cleaning. It did help a little bit.
When it arrived the sensor was very dirty. Canon must shame itself a little bit for delivering a top tool as dirty as it was. Altogheter I've spend several hours to clean it, but the dust is very difficult to remove. It is now on a acceptable level, I don't have to remove 50 or more spots a frame anymore.
For the rest, great camera with an outstanding autofocus.