first things first, do you have any solid reasons why you shouldn't take the job? Do you have, or do you plan on getting your CPA?
i finished grad school with a masters in accounting and worked with DFAS for awhile on a systems implementation and the government is a great place to work. i ended up leaving because i would be relocated and my girl is a doctor with an established practice. it was easier for me to start something new than it was for her to try and build a new practice.
bottom line, it's a great place to launch your career. even if you only work there for 5 years, it's going to be great for your resume. i wouldn't even think twice about not moving forward with this opportunity.