Career mobility is sometimes constrained within certain departments. This forces individuals to look to other departments for new opportunities to advance their careers. This can be disheartening to some. In a company so large, it takes real effort, a record of strong work performance, and maybe sometimes just knowing the right person to get ahead. Otherwise, one can really fall into a rut-- easily finding themselves working in the same position for 6-10+ yrs.
Another negative (and this could just be my personal perception of things) is the limited amount of salaried positions within the company. Many jobs are part-time, thus leaving individuals with families and responsibilities of their own to work egregious amounts of overtime. This might not be as much of a concern for the new career professional though.