Pros
By far one of the best staffing companies out there. I've been there now for a few years and can easily say that the people who work in cooperate and out at customer sites are some of the best folks around. Their recruiting team is always on-top of keeping their employees up to date with new positions within the company and they are always there to help out with any needs or issues that their employees may have. They definitely have industry knowledge as to where the customer is heading with technology, budget, re-competes, which puts me at ease with having job security. Company culture is huge, very family oriented (which is nice for somebody that has kids, like me), decent amount of company events to attend if you want to get to know some other folks outside of your cube that work for the company.
Cons
Did some transitioning with Paychex, and contracts which wasn't easy but has smoothed out much better now.