Ventajas
Working at Lockheed Martin is like having a part-time job, with full-time pay. I've been there for over 4 years, and have never, ever worked more than 40 hours a week. As a software engineer, you have enormous discretion over when/where to work. Since I can get the job done quickly, I probably make it to the office for only 5-6 hours a day. Combined with the 9/80 schedule, it's like having 3-day weekends all the time. The work can be interesting at times, especially since you are working with complex electronic systems.
Desventajas
The technology is older than at most Silicon Valley companies, so don't expect cutting-edge research/development. Some of the buildings don't have windows, so that sucks too. Also, most employees are pretty old.