Pros
Fresh out of school, I think it would be a great place to explore because there are so many different IBMs. There are opportunities to work in almost any part of the globe and in really excellent fields like fractals. IBM also has a lot of presence in Second Life, which is a lot like having the company's blessing to play games!
Cons
If you're acquired later in a career, and there is nothing similar, they don't necessarily know what to do with you, and it's really up to you to try to dig yourself out of miscategorization. Also, since it is so large, if you're used to a small company where it's easy to make sure everyone knows something, the 'pull' culture at IBM is tough to get used to - w3 is a great mass of information that you're expected to navigate for yourself.
