I former co-worker of mine told me about their priority tracking software where you could enter a number from 0-5 for each bug, where 0 was the highest priority and only certain senior managers could set a priority of 0.

However people soon discovered that priorities where stored as a float in the database and they could enter any number 0<n<=5 in the field. So bugs quickly started to get priorities like 0.5, 0.25, 0.1, 0.05 and so on...