Pros
The pay and benefits package is good for the area, a good chunk of the day is spent outside with the (mostly) appreciative public, and you don't need a college degree or specialized training. Work doesn't follow you home (or away on vacation). The work itself isn't difficult, and as long as you show up and do it, you should be fine.
Cons
I'd almost describe it as the love child of "Catch-22" and "The Office." Management is clueless at all levels; antagonism between management and craft (the workers) is pervasive and seriously affects morale; there is no-to-little sense of working for the greater good of the company, that bright ideas or attention to detail or careful analysis is appreciated or even desired. This isn't the worst place I've worked as far awful corporate culture goes...but the others all went out of business, and I'd hate to see that happen to the Post Office.