Pros
If you love a particular technology, then you are the only limit to how successful you want to be. ACN is a huge firm that affords a tremendous amount of opportunity to individuals. I was allowed to travel quite a bit during my analyst years (even overseas), which was an incredible experience. You would be hard pressed to find other firms that allow you such latitude in work location and job function. Management always tended to be supportive of what you wanted to do, especially if it fit in with serving the client. Additionally, if you were on a services-focused account, your work schedule could be pretty flexible.
Cons
Rigid processes, but that is what makes the company so good for clients, and for investors. Also, you tend to get pigeon-holed into a technology, or process pretty quickly. If you don't watch out, you could be three years down the road with the firm and working on a technology that is going to be obsolete in a couple of more years. Although the firm provides a lot of opportunity, you need to be actively managing your own career. The company tends to make training widely available; however, you'll need to be savvy enough to convince your HR rep that you merit the firm spending that money on you.