Ventajas
Lockheed has a lot of contracts to work on in the DC area. They do a lot of different kinds of work. You can always find the technology you want to work on somewhere within the company. The people are generally great to work with. Working with government types is a great experience. There are an abundance of training options, and the best educational reimbursement I know of in this economy.
Desventajas
Your work location may change on a whim. You won't always work in the cleanest of facilities. The amount of restrictions you have can become burdensome at times. The pay is low compared to other companies, but there are a lot of opportunities for promotion and growth if you put extra effort into it. There is way to much management. A lot of managers seem to not have a general competency in the technologies they oversee, which is frustrating. Bonuses are awful. Lunches are terrible.