Pros
Good core business in audit and IT audit. You could do very well and be successful if your specialties are aligned with Protiviti's core business. It can be tough if you have a specialty outside the firm's core business. People who stick it out and suffer through the lower ranks will eventually get promoted (sometimes rather quickly) and will get paid very well.... but you do need to suffer quite a few years first. If you stick it out, long term it's a great place to be.
Cons
Hours can be extremely long (nights, weekends, travel) and compensation doesn't necessarily match the commitment. People (in same peer group) are paid more or less the same (+/- 5K) regardless of whether you are top performer or bottom performer. Very little incentive to go above and beyond. You are incentivized to be mediocre and as a result there are very many mediocrities at the company. The bottom people often get laid off (up or out) and the top people sadly leave for better opportunities.