I don't seem to get sore knees unless i stand still for extended periods of time.
My knees are fine when I skateboard or do exercise though so it made me curious.
EDIT: I skateboard for more than 4 hours and am fine afterwords. I only get the pain when I stand still in one spot. For example, if I stand at the computer for 4 hours in the same position then my knees will be sore.