Ventajas
The 9/80 work week is great. It takes about two weeks to get used to, and then you wonder how you lived without it. They are very flexible with work hours (generally; depends on the project) and overtime is available and paid at 1.5 time (again, depends on the project). Medical/dental/vision benefits are great - BCBS. Positive future and stable business - hopefully in spite of the government administration changes and economy downturn.
Desventajas
As with any huge company, we are riddled with bureaucracy and process. We are working to achieve CMMI level 4 (currently a level 3), so we can expect more processes and more paperwork to slow the actual work. Performance ratings are meaningless. You really aren't rewarded for your good work, other than your manager patting you on the back. As long as you aren't dumb enough to get formal discipline, you'll get an average rating. If you work extra hours and do twice the required work, you'll get an average rating. So, it's a nice place to find stability regardless of effort.