Ventajas
Lockheed provides a secure job. Many employees have worked here for over 10 years. I have worked here for 7 years, and have never worked overtime. They are flexible with work schedules - I work four 10 hour days per week. They are always well funded, so I usually don't have to cut corners in my work or step over trash in the hallways. The software development is usually interesting because the company focuses on large scale, high tech national defense products.
Desventajas
Process, Process, and more process. Its hard to sneeze without filling out some spreadsheet form and submitting it to a committee. For the most part, you don't have much freedom in choosing tools or design approach. However, if you are very passionate about changing something, you can go through all the red tape to make it happen - Ive done it. They just make it very difficult. Also, since the programs are very large, you become a very small cog in a very large device. So, you learn very little about how the rest of the world (real world?) does software development.