Pros
Protiviti is an unique place to work because its smaller than a big four, but bigger than boutique shops. This results in a place where you'll learn a lot in a short amount of time, with as much as handholding in the beginning as needed (within reason). The base salaries are slightly under what you'd find at other consulting shops, but the bonuses, which are based on chargeability and project performance, are pretty good. There are many ex-Andersen veterans working here, which equates to working with some of the best and brightest in their respective industries. Of course with any workplace, there are star performance and complete morons, and often times its hard to distinguish the two at first.
Cons
Protiviti has recently completed a series of 2-3 rounds of layoffs, citing "market conditions". I will not discuss of their choices of termination here, but the cuts definitely served to lower morale around Protiviti offices nationwide. This, combined with lukewarm raises given last July, equates to unhappy employees.