Pros
The work is as cutting edge as it gets. As a software engineer, I was exposed to a multitude of technologies that were just taking off. The environment is relatively informal. The hours are extremely flexible. I could just not go to work on a random day of the week and that was ok as long as I sent an email.
Cons
It is nearly impossible to be promoted above a level 3 engineer in the Advanced Technology Lab. The level 4 and 5 employees aren't going anywhere, and there's not enough lower level employees to justify promoting any more 3's. It's purely a function of the lack of breadth in the 230 person organization. Also, unless you are coming in with a PhD from another high paying job, expect to get less than industry standard. People are leaving the company now and getting at least 20-25% pay increases.