Ventajas
Lockheed is a great name to have on your resume when you're looking for a better job. As far as actually working at Lockheed, it's a huge company doing mostly government contracting, so it's somewhat resistant to economic swings, but there have been layoffs in the last year.
Desventajas
Most the people in management at the Manassas site are holdovers from before the site was a Lockheed facility. These people are entrenched in their jobs and are resistant to any change. There is an incredibly strong "good ole boys" atmosphere, and it is next to impossible to advance if you're not part of the club, or willing to do some serious brown-nosing. This also leads to a culture of employees being fearful of reporting anything that's unfair, unethical, or worse out of fear of retaliation. Lockheed uses a forced ranking performance assessment process which drops employees into five performance categories, with well over half getting the middle "successful" category. The performance evaluation criteria are intentionally extremely vague so that management can justify giving anybody any assessment. Even with such a wide open system, the managers don't even bother to make it appear that they actually follow the system to evaluate employees. I know from looking at my manager's publicly available Outlook calendar that the managers finished ranking employees in my department last year BEFORE the peer and lead ("multi-raters") input was collected. They didn't even bother to hear what coworkers had to say about us! They just got together, sat in a room, and decided which employees they liked best.