Pros
I was one of 50 interns at Lockheed Martin Space Systems summer 2010. In speaking with many of them, I'll point out that our experiences were not the same. I don't believe one could generalize the "Lockheed Martin internship experience." I know of interns whose managers brought them in w/o a clear assignment in mind. My experience was quite the opposite. My manager knew exactly what he recruited me for, and the work was lined up for me the moment I walked in. In fact, I couldn't truly finish it all over the course of the summer, but I think that was expected. It was technical, required courses from my major (EE), and was certainly "real." By that I mean it was integrated into the larger project of my group, and not tossed aside after I left.
My experience was a good one:
-good pay
-good work
-good location
-friendly people to work with
-great manager
-opportunities to learn (they sent me to philly for training!)
-opportunities to network
Cons
Here's the tough part: I was only so-so on the work by the end of the summer. That was due to the nature of the group in which I interned. I think a lot of work is like that at Lockheed, or any large (defense) company. You have to hunt to get the interesting stuff.
other cons
-cafeteria food was meh
-they'll bring me back for more blah work
