Pros
Given Protiviti's size, employees have a unique opportunity to participate in various capacities (e.g., methodology development, business development, project management, internal initiatives, training). Additionally, you will interact with some very good managers who respect their staff. Lastly, Protiviti does not burn-out their employees (although that may change with the cost-cutting measures taking place and the work starts to pile on the remaining employees).
Cons
Senior management and legacy employees tends to keep chargeable hours and relationships for themselves. This hurts junior managers and makes them expendable. Additionally, if you do not have a niche or speciality that supports what sells in the market at the time, you are vunerable. You may get piegeon-holed quickly, so make sure you identify a niche early on and pursue it aggresively.