Pros
Great network and potential if you can work out how to make the most of it. Nice name brand recognition, though usually for the worng reason for services. Some good people there, but I would have to say the minority. In 11 years I found 1 good mentor.
Cons
Many policies (such as accelerated management programs) unknown in GBS. Viewed by the rest of the company as a cash cow, so without being in the 'line management' network very limited scope for advancement. IBM will always be first and foremost a 'slinger of iron', such that you always have to explain the value of IBM GS as a management consulting service provider. 50% of potential clients dont get it and never will. The model is changing, with services following the big captive deals rather than being the 'tip of the arrow'