Pros
As a large company, you have the freedom to move around between a lot of different projects, and this is actually very encouraged (as far as corporate policy goes). They're fair about these transfers, too - they like to stay in one place for a reasonable amount of time before going to another group, but otherwise no one can really stop you from doing the kind of work you want (provided it's available and you've got the skills for the job). They're also very aware, as a corporation, about their poor retention of young workers and engineers, and act accordingly by encouraging mentoring, sponsoring affinity groups for networking opportunities, and funneling strong talent into development programs.
Cons
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.