Pros
There are a few good reasons to work at IBM. The first is to establish a higher base salary for yourself which you can advertise to your next employer. Get in and get out. The second good reason to work at IBM, at least as a consultant, is you do learn a lot in a consulting role. This theory applies at any consulting firm though, so not particularly strong seller for IBM in particular. If you are lucky as I have been, you will make some great friends as well on the road.
Cons
Travel is extensive. "Work-life balance" is totally lip service. The only thing that matters to this company is sales and as a result, the only real bonuses go to sales people. Oh yes, and they use forced rankings, which means someone has to fail. I was fortunate enough to always have a high PBC rating (of course not high enough to get any decent bonus though). Raises are a pittance if non-existent. Their approach is flawed. They oversell commitments, even those that we have zero experience with. Their theory is to just throw bodies at any problem, and as such, you will just become a resource. Another number. Another worker. Additionally, you never know when/if you might be layed off. You will have to travel a lot, get little to no salary increase, little to no bonus money, little to no work-life balance.....well at least you get some job security right. Not exactly.