Young talent flees for good reasons - the pay, when compared to other companies in Silicon Valley, is regarded as below par. The most talented engineers, if they come straight out of school, tend to leave within the first 5 years for greener, more profitable pastures. The result, whether senior management recognizes it or not, is that in the middle ranks there's a huge dual-peak spread of abilities. If your manager is stellar, chances are she was bright, talented, and got just enough experience to be able to ascend quickly and do a great job. If not, she's probably just a rather mediocre person who happened to have enough seniority and institutional memory to be promoted. And the manager you get is just luck of the draw.
Additionally, the size of the corporation is a double-edged sword; even though you can work on a lot of things, chances are good you'll feel like a cog in a sporadically well-oiled machine. Furthermore, many of the projects are "legacy" projects that stifle innovation, or new ones that get tied up in political (read: government funding) knots for ages. Both cases make it difficult for an engineer to enjoy his or her job.
Lastly, LM retains a certain amount of "boys' club" atmosphere. While this is of course frowned upon by corporate, this environment permeates throughout, more so than in younger companies. If you're a young woman, I'd be wary - not for sexual harassment reasons, but gender/pregnancy discrimination ones.
