Prós
The company has a wealth of information and experience that form an excellent foundation with which to start a career. The knowledge that can be gained in working with some of the older, experienced engineers really is priceless. Lockeheed's benefits package is extremely good. New hires (at least within Aeronautics) are receiving three weeks vacation per year. Aeronautics is also on a flex time, 9/80 work schedule. Employees on the 9/80 schedule work 9 hours per day and have every other Friday off. Flex time must be worked out with your individual supervisor, however core hours (which everyone must work) are from 9 am to 3 pm. The hours each employees works outside the core hours is largely up to them as long as 40 hours are worked per week.
Contras
Lockheed is an extremely large company and as a result, building a name for yourself and getting noticed within the company can be more difficult than at smaller companies. That is not to say that you are not rewarded for your work, but that a little extra effort is needed.