This turned out to be the solution for me.
For me, the Dock app was looking for a DefaultDesktop.jpg file and coulnd't find it. Chewed up to 75% CPU trying to locate it.
Thanks for your handy tip, I was able to see what the Doc was looking for.
To fix, for me, was to go into the System Preferences, launch the Desktop preferences and simply pick an image (any image) for the Desktop.
Then, went into the Monitor application and did a Quit on the Dock app.
Doc restarted and is back down to using ZERO % CPU.
All fixed now.
BTW : This particular system doesn't have Parallels or Fusion installed - so I knew those weren't the issue. Issuing the opensnoop command really helped!
Update. Using 10.7.2 …. I've done everything suggested in this and other posts about the dock using too much memory. Deleting the plist, etc. worked twice, but periodically the dock ***** memory like crazy and the fan goes crazy. Whats working since is then is to repair permissions and either logout or reboot. Has worked every time so far after a month or so.