Pros
Policy, rule-making, and interpretations are the mainstays of what gets done at the SEC. Being on the front lines is exciting and watching the changes being made in the interest of investor and public protection is extremely interesting. It is very different from working in the private sector and knowing that you are working towards a common goal and a "greater good" is both motivating and unifying. I got exposure to many different accounting issues and loved the people I worked for. The SEC has interesting seminars and workshops for the interns, but what was even better were the trainings available to all employees that took place multiple times a week and were about many different topics.
Cons
The pace is slower so if you want to be in a faster moving, higher pressure environment, then the government is not the place to look. It is also frustrating when certain initiatives are dropped without warning and hard work over the past couple of months ends up being all for naught.