Pros
The education a company life IBM conprovide for employees looking to re-tool is powerful - especially in sales and management... but watch out if you're in a service delivery role because it's very challenging to get training there. The benefits are outstanding, time off for critical family issues is really remarkable but overall work/life balance is better than average.
Cons
In theory IBM should have tons of opportunity for growth (different divisions, many countries, etc.) but you get pigeon holed quickly, and find its very difficult to move up. They are like the ancient roman army or something... they just assume when the first line goes down there's tons of people to step in so you only move up by out-lasting your competition (who probably left for more money and challenges somewhere else).