I was having the same problem with the Camera Depth pass as you J.P., and searched the forums and google FOREVER trying to find the answer to the issue that was driving me crazy. This is what I came up with to fix my problem.
While I was reading through the Maya 2009 Documentation I remember reading a line that said “blah blah blah turn on Remap Depth Values blah blah blah.” So of course the first thing I did was go to the Camera Depth pass and clicked that check box. Welp, after spending about a day and a half trying to find an answer it turns out that little check box was the problem the whole time. All I had to do was open my render settings window, open the passes tab, double click on my “depth” (Camera Depth) pass to bring up the attribute editor, and uncheck the “Remap depth values” box. I did a few tests with adjusting the near and far clipping planes, but in the end the default 0/1000 worked just fine.
Let me know if this helps you out.