Pros
Looks good on the CV, with some household (FTSE 100) names on the books. Exposure to both public and private sector customers with the chance to work across the full spectrum of the solution life cycle; pre-sales, design, delivery, service etc. A family friendly company which is surprising for a global IT company, plenty of support for work/home life balance from management with good benefits such as company cars or car allowance, health care, pension, insurances etc (role dependant of course).
Cons
Networking is key for career progression, company is so vast that you can easily become a small fish in a large pond and go unnoticed despite constant certification updating (self funded), regular 12hr days and fantastic customer feedback. Assignment based work or in other words a contractor based approach, can be working with one customer for 10 days and never see or hear from them again, sometimes this is an advantage if the customer is a pain, on the other hand it's hard to become a trusted advisor and create long lasting relationships...low job satisfaction. Training is few and far between with architects sold as "experts" to customers when in reality there is little time or budget for self study, certification or training, "I will take that offline and come back to you" is a phrase you will often hear yourself saying to customers in meetings. Salary is relatively low but other benefits such as dictating your work location make up for it somewhat.