If you use wmmon dockapp, the CPU stress meter shows the average of all processors. So if a processus takes all CPU on one processor, you don't see it. That's why i decided to patch wmmon for a better SMP machines management.
Of course, if the machine has only one processor, visually there is no change.
Otherwise there are two possible views:
You can see the activity of the four processors.
The average is approximately equal to the max. This means that all processors are used approximately similarly.
Even if all processors are not used, there is a processus that takes all the CPU time on one processor.