I joined IBM when I left Uni, and stayed there for about 6 years.
I was a great company to start my career with. I was exposed to the whole spectrum of managing large scale software projects, from bidding on $100m+ contracts through implementation, change management, on site comissioning (I once spent 6 months doing 70 hour weeks in an underground nuclear bunker commisioning a safety & security critical system for the RAF...), through to post delivery support.
You'll be pushed hard, and no-one will do anything for you - promotion is gained through application, rather than being given to you - you have to prove you're good enough. On the upside, the rewards are great - especially if they're still running the share options scheme....
Like you will be, I started as an IT Specialist trainee, then moved through Entry-level IT Specialist ,m and onto Advisory IT Specialist by the time I left. It set me in great store for my career from then on - IBM is a great name to have on ones CV.
I would suggest one thing though - IBM doesnt have the best reputation for continuing to value people over longer periods - there's a surprising amount of folk who are 'returnees', who've gone to other jobs to contnue their development before returning to the fold in much more senior positions than they would have reached if they'd stay put. Just bear that in mind....
Edit: Oh yeah...Lotus notes. It both sucks *and* blows.