Pros
Technical challenges are current and proved opportunities to work in a dynamic environment. When CSC bought out an existing company I worked wtih, it felt like the new company was not concerned with the existing business arms that were established, even if they were profitable and had local support in the defense community. It was a very secure feeling working for a large company that had their processes and benefit structures well known, and policies in place to protect and encourage employee professional development.
Cons
It's so big that you feel detached from the large decisions of the company. It always felt like my line of work was not important to the company, and there was not the business development support to help our small successful group grow.