Pros
I joined IBM though the Graduate programme. This has a strong focus on skills development. Each graduate completes more than 6 weeks of training over the two years and is assigned to a number of different projects to provide a variety of experience. The career prospects are good at IBM, you have the opportunity to move into a variety of professions, providing there is a business need. You have continued support from management to meet your goals. They have a big focus on work life balance. Most importantly, working for IBM looks good on your CV should you ever want to leave.
Cons
IBM is a large business, like most corporations it is very much process driven. To complete the simpliest of tasks, something that could be achieved in ten minutes at a smaller company can take up to two weeks to complete. This is not only frustrating but can also be embarassing to client and supplier teams who are much more agile. Also, there is a lot of game playing at IBM, if you want to go far, you have to be prepared to play the game. You won't be rewarded for doing your job well, you have to be preared to network with and influence management.