Pros
Due to the enormous size of the company, it is sometimes easy to hide behind radar screen so works are not usually too stressful. It will be great if you are near retirement or you don't want to sweat at your job. If your job is in the field of technology, you may be able to get your hand dirty with the latest technology at your employer's expense. Another good thing is that you got cheap landline phone service, 50% of iPhone monthly fee and 50% off U-Verse TV!
Cons
Difficult to get a promotion or change to different jobs. What I dreaded the most is that when your applications to another internal openings are turned down, you don't even get a feedback on why you were turned down and what you need to work on. And also because the company is so big, your responsibility can be very narrow and it can be boring after a while. Although we have mandatory performance review throughout the year, we all realize that it does not mean anything but we have to do it anyway to fulfill some policy. Everyone got a "good job, well done" but it does not mean you will get a promotion or even a pay raise. Can you believe that I have to write my review and to be approved by my supervisor? Do they expect me to give myself a bad review?