Why programmers are not paid in proportion to their productivity — The Endeavour
I like that view :) ... mostly what I think and experienced so far.
So be aware if a programmer leaves your company after a "short" (would say 1 year) time it's likely because his skill is greater than the skill of your other coders. I've worked with bad coders and it's very frustrating if you have to explain obvious simple concepts again and again.
It's hard to notice these things as they usually will never state that they are frustrated because of the skill of other coders at the company. Especially team managers should always have an eye on that one ... I think regular personal talks can help there.