After installing the recently released OS X 10.6.8 update for Snow Leopard, many people are finding their systems running a bit slower than usual, and upon checking Activity Monitor are seeing that the Dock process is taking up 100 percent of the CPU. This problem has persisted even after people have reset their Docks by removing the Dock's preferences and database files, in addition to performing other common tasks like running permissions fixes, performing hardware resets, and booting to Safe Mode.
The problem appears to be an incompatibility with Parallels Desktop 6, which has an option to make Windows applications available in the Dock for convenient access. This incompatibility will likely require an update from Parallels to fix, but until then one option you have is to disable the Dock applications setting for each virtual machine you have configured:
Open Parallels Desktop and show the list of virtual machines.
Shut down any virtual machines if they are running (do not merely suspend them).
Right-click each virtual machine in the VM list and choose "Configure."
In the Options section select Applications and uncheck "Show Windows applications folder in Dock."
Do this for each virtual machine you have set up, and you should be good to go. Hopefully Parallels will release an update to its software to address this issue.