Pros
The pay is good, they hire pretty cool people for the most part, so it's easy to get along with everyone. It is a cool job if you want to travel around the United States for really long periods of time. Most of the employees are young, recent college grads which makes a high energy atmosphere. There is a semi-vacation every year taken by the whole company which is cool.
Cons
The cons definitely outweigh the pros. The hours are extremely long sometimes (most of the time). I'm talking mandatory 10, 11, 12 hour days. And a lot of weekends. When you aren't working, Fast holds a lot of get togethers outside of work, all of which involve drinking. If you don't like to drink, you will be the odd man out. Time off can be difficult to get sometimes. Some sites are worse than others, it depends a lot on the project manager and the other Fasties on the site. The technology you learn is very proprietary, and my programming skills have definitely gotten worse since I've been with fast. Visual Basic and SQL are pretty much it.