Vantaggi
Most all of hte people I've worked with are intelligent, friendly, and willing to teach / help. Promotions are merit based (for the most part), so if you do a good job you will get noticed. Not quite as politic-based as I've heard from other firms. The variety of clients and service lines has allowed me to see quite a bit in a relatively short period of time.
Svantaggi
Protiviti doesn't always staff the projects in the most logical way. Flying halfway across the country to do general work (that most anyone could do) never made sense to me when we had a local office in the same city. Staffing seems to be done mostly at the regional level, and the regions don't always communicate well with each other. Depending on the project and deadlines, stress levels can get pretty high, and the hours can get long. Also, the pay is not quite up there with some of the other larger consulting firms, but in the down economy I should be happy that I still have a job.