I tried the current Mac beta on two different Macs, one with 10.6 the other with 10.7. In both cases, the software recognizes the 1D X, but trying to connect to it force-quits the program. Do note that there's a quirk (detailed in the instructions) that you must select either Canon or Nikon in the Preferences - even though Canon is the default setting, you must actually re-select it. Before doing that, it wouldn't recognize the camera at all.
I will troubleshoot further when I have time, but it's not high on my list of priorities - the 1D X must be run in manual settings change mode anyway, so for me it's just as easy to shoot a series of AFMA shots (I take 83 of them, 2 shots every 2 units from |20| to |12| and 3 shots every unit from -10 to +10, and that takes about 10 minutes). I then analyze them with FoCal in Manual Mode, and that runs fine on the Mac.