I was taken out to dinner with around 10-15 other candidates. I then had an on-campus interview which lasted 45 minutes. The questions were pretty straightforward, behavioral based. (i.e. Tell me about a time when...) My interviewer recommended me for the Sales Territory Management position, at which point my name entered a pool of candidates from all national universities.
I contacted my recruiter and RPAT to let them know that I had another offer deadline, which I believe expedited the hiring process. They flew me to Fairfax and had three 45 minute interviews as well as meals with a host. The interviews were again pretty straightforward and behavioral based. I think that if you get an on-site interview, they mainly want to see 1) how well you fit with the company and other employees and 2) how well you present yourself.
Overall: Not extremely stressful/difficult interviews, but a lot of work to get an interview