Pros
IBM can accomplish amazing things when it puts its collective shoulder to the wheel - applying consulting insight, real original thought leadership from IBM Research and a sales organization that is focused on customer success. When those capabilities are aligned, some real transformative work can be accomplished and can be a "once in a career" opportunity.
Cons
For most situations, IBM has put innovation and business insight off to the side and focused on lowering the cost of service delivery, which means providing more services remotely from India (and where ever else labor arbitrage will lead), less US-based consultants, but more stress on the consultants that remain, increased reliance on sub-contractors and limited opportunities for career growth here in the States. Competing on cost rather than quality increases the risk of "troubled" projects and, with the flat economy, there is no job security at any level.