Bev, youve hit the nail on the head.
A Cpk on its own is surely only showing, possibly, half the story. It needs to be used with PPMs or DPMO figures to fairly represent the process.
If you are going to report just one number then surely the Zbench score is a better measure to use instead of Cpk scores.
Of course if I wanted to throw something else into the discussion how about the switch of Cpk, Ppk being refered to as short term or long term. Depending on who you talk to.
The other great confuser in all of this is the sigma shift issue. Which alone is enough to make anyone start to twitch. Had plenty of fun discussions on that, why are you adding/removing 1.5 sigma? what logic are you applying there?