Pros
The only reason to work for the US Postal Service is money/benefits. There are not many jobs in todays market that pay as well as the US Postal Service without a degree. You will work long hard hours for the first three or four years. Things get a lot easier once you have a little time under your belt. The insurance benefits are great, and you can choose from several different plans. Although there is not a civil service retirement you can still contribute to the governments version of a 401K. This is actually a great deal with matching contributions.
Cons
If you want a nine to five job, this is not the place. Overtime is almost always the case. This is great if you want the extra money, but when it becomes mandatory nearly every day you can get burned out very quickly. A lot of people actually get used to the overtime, and count on it to pay the bills. This can be a huge mistake! What the US Postal Services giveth they can take away. Managment usually consist of people that have never done your job, and yet they tell you that you are doing your job wrong everyday!