One thing to try is to temporarily remove the Dock preference files & see if the CPU badness stops. Try this in Terminal:
mv com.apple.dock.db com.apple.dock.db_backup
mv com.apple.dock.plist com.apple.dock.plist_backup
Once Dock.app restarts it should open with only the default set of icons. Depending on the presence of installed Apple apps, (iWork, iLife, & etc,) icons for them will be created in the Dock for them, too. You will also have to reset your Dock preferences and add other apps as you see fit.
If you are satisfied with the fix, and the Dock doesn't hammer the CPU, delete the old Dock preference files which caused all the problems:
On the other hand, if you wish to restore the original preference files for some reason, do this:
mv com.apple.dock.db_backup com.apple.dock.db
mv com.apple.dock.plist_backup com.apple.dock.plist
Troubleshooting tip: Alternate between the old & new preference files & restart the Dock to see if the CPU is hammered. If a restore of the original preference files causes the Dock to misbehave, something in one or both of the two files is munged.
On the other hand, if the Dock still hammers the CPU with fresh preference files, something else is amiss.