Pros
You will get many opportunities to learn, grow and get involved in activities sponsored by the company (if you have the time and energy which you might not). Clark is great for your resume as well, especially if you live in the DC area where the company is well known and well respected. Clark opens many doors because it has a culture of over achieving. Clark believes in doing everything the hard way and always going above and beyond. The main reason this is good is because once you leave Clark, your next job will be easier and you will probably make more money doing it. Great place for recent colleges grads to "pay their dues". Clark will toughen you up and you will thank it later. If you can make it at Clark, you can probably make it at most places.
Cons
There is nothing wrong with a hard days work. But Clark can take this to the extreme.The company definitely shows its age with is many old fashion ways. If you are not unusually intelligent, an over-achiever or a workaholic, then you might not enjoy working at Clark. These are really the only personality types you will find (who have lasted long). The culture is very formal and pretentious. No casual Friday (in the Bethesda office). Clark wants you to work until you drop.. then work some more. You will work long hours as sure as the night is dark. Clark does not want anyone who just wants to come to work and go home. Expect to think about work all weekend if you are not actually working on the weekend. You might be. There are strict rules and processes for doing your work and you cannot deviate from them. Sometimes these rules lead to inefficiency. You will burn out fast and get sick often if you don't set limits. Clark will work you hard. Clark does not believe in doing anything the easy way. Stress levels can be high and you will see more frowns than smiles throughout your day. Pay is low for what is expected of you. Clark does not close for bad weather or most other things. Not much PTO days until you have been with the company for a long time. But you probably won't have time to use them anyway.