A long time again, on a PC far far away I used to play Ultima Online, one of the first and, in my humble opinion, one of the best MMORPGs ever made.
It ran on a system of skill points. Each character could gain up to 700 points divided among all the available skills to a maximum of 100 in each. As you performed certain tasks, that skill had a chance of being increased do to usage. The funny thing was, if you had already gained all 700 skill points and gained another point in a skill, it would take a point away from your least used skill. This was to simulate an atrophy of skills that are hardly used in favor of those that are used often.
