Hi robacz,
Just wondering what the settings of your dock are...
Do you have it set to autohide? If not, do you have it set to bring itself to the front when the mouse nears the edge? Which edge is the dock on... the same edge as another bar/taskbar, or some other otherwise-uninhabited edge? Do you have a multimonitor system? And if so the dock isn't on an edge that boarders another monitor is it?
Regardings effects/color, what color is your dock set to? "Glass", "Default/black", or some custom color? And which effect do you have in use, the default "grow" effect, or the "swing" or "glow" effects? Is the dock "Locked" or in "Touch Mode"? (All of these settings are viewable from the settings panel in the dock)
Finally, do you have enough items on your dock where it needs scroll-arrows? Or does it all fit nicely on the screen.
Sorry for all the question, but have no idea exactly why it would take that much CPU and so trying to get enough information to perhaps get a picture! Thank you.