Pros
After the initial steep learning curve, the job is pretty easy and pays well. The pay is based on the evaluation of the mail volume on your route (generally evaluated once per year). So a route might be evaluated at 45 hours per week, but most carriers can do their job in less than 40 hours, so you are basically getting paid 45 hours for less than 40 hours of actual work.
Cons
Constant (at least weekly) reminders of how poorly the USPS is doing fiscally. The threat of a 5 day delivery hanging over the postal service. Incompetence at the higher management level. The mail handlers at the main plant do not sort much of the mail they are supposed to sort, and since it must be delivered by a certain time, it usually gets sent to the carriers to sort. This takes much extra time, but all too conveniently, this never happens when the yearly mail count is going on.