My wife and her friend took the postal exam on a lark and both passed without doing any preparation. A few months later they were contacted for part-time positions as letter carriers, and they heard through the grapevine that it was very likely the route would be a walking route in bad urban neighborhoods. The positions are by seniority so as soon as someone has been there long enough to get a better route (especially one where you just drive), there are openings in the crummy assignments.
IIRC, the job paid over $17/hour.