Pros
ACN has a good reputation in the IT sphere and can provide various opportunities across different sectors of the government. It also has a strong corporate culture and is very institutionalized in that way; I came from a much smaller firm and enjoyed the increased "systematic-ness" of ACN vs. the much more ad-hoc daily workings of a smaller company. While I do appreciate the advantages of a smaller firm in certain ways, ACN could leverage its size in many ways, internally and externally. The salary was also good--ACN offered me almost twice my salary from my previous job. Travel benefits were good as well.
Cons
The travel was extremely heavy. I was flying to the client site every monday, flying back home every thursday evening, for 6 month stretches. Not exactly a great situation for someone with a home and/or family. The work itself was also fairly monotonous; maybe for someone with an extensive IT background it would have been more interesting, but working on spreadsheets for 80% of my day was not my idea of "adding value." I did have access to the primary client as a junior consultant, but the numbers/spreadsheets ran the day; almost no real intuitive thought needed.