Applied online directly through their website. Heard back the following week and scheduled a phone interview with an campus recruiter. The recruiter is just trying to get a sense of your personality and whether your past work experiences are applicable to the position you applied for. Really laid back and conversational. Later that week I was invited to an in-office visit the next month.
The in-office visit was very professional. There's a pre-interview dinner the night before and they put you up in a very nice hotel that night. The in-office visit consisted of an hour-long presentation about Protiviti, followed by two 1:1 30-minute interviews with directors and managing directors. Again, these interviews are very basic and conversational. You're just asked a few behavioral questions and then go over your resume. Be sure to come to the interviews with questions already prepared. After the interviews, they take you out to a nice, long lunch with the other applicants. You finish up the day with a group presentation on what you've learned about the company. I received an offer the following day.
Just be yourself during the entire interview process. They're trying to gauge whether you can work well on a team and if your personality meshes with the young, energetic culture of the firm. Everyone in the office is very approachable and easy to talk to. I definitely felt at home by the end of the day.