Pros
You will never be unemployed if you have IBM on your resume and you are good at what you do. Good internal training opportunities, and sales training is the best in the world. Good way to learn the fundamentals of processes and taking ownership. Great benefits, such as higher super, empoyee share plan, retail discounts etc. Excellent job security for women who take time for babies, and if you are a mother (I wasn't) all of the work/life balance initiatives are designed for you. You can actually come across some the most gifted and talented work colleagues and mentors who can assist you in day to day and in professional growth.
Cons
Quite often promotions are more based on who you know, not how good you are. If you are on sales quota, you will NEVER understand how you get paid, and neither will your manager, or the commissions help team. Excessive pressure at end of quarter, where often your job security is questioned, regardless of your ability to do the job. (ie: team not hitting quota, but you are). If you are effecient, there is often frustration in getting tasks completed, as bureaucracy is heavy going. If you a single person, looking to advance, there is an expectation that you work ridiculously long hours to prove yourself (especially compared with colleagues who had children, and who have work/life balance).