Pros
In fairness, if you are looking for a secure job, it's the federal government and it isn't going anywhere. Also, it can be a power trip, and many of my colleagues seemed to relish the control we had over various small businesses and individuals. Finally, if you're trying to raise a family and just want a 40-hour job, doing the same thing day in and day out, but often enough flexibility to care for kids, etc---some people think the tradeoff is worth it.
Cons
There is no room at all for creativity or efficiency. Imagine how open the IRS is to new ideas when you're doing your taxes---they bring that same rigidity to all aspects of the job. Also, since nobody but nobody in the federal government is going to advocate for the IRS, they usually get the worst working conditions and facilities, compared to other agencies.