(Actually interviewed in October 2008)
Process started with applying online through Careerbuilder.com. I was contacted by a recruiter who then described the position and set up a follow up phone interview with me for the next day. The phone interview was a basic pre-screen for the position that lasted about 20 minutes. They make you aware that you could potentially be relocated, although they often will try to work with you to make sure you are willing to move to wherever they want you to before extending the final offer. DO NOT state you are completely open to relocate ANYWHERE if you are NOT - they will take this literally.
After the phone interview was completed I was contacted to schedule a day in the trade with one of the local reps in my city. I rode along with the rep for a half day to see what a typical day on the job entails. At that point the rep reports back to the company (they don't tell you they do this, but they do as I have executed days on the trade during my tenure as a rep) on your general attitude and their opinion of how you would or would not succeed with the company and why. Although these reports are not weighted very heavily, they are taken into account.
After the day on the trade you are asked if you are still interested in the position - several people will drop out of the interview process at this point because they do not like the job, so it's a great portion of the job to see if you indeed are compatible with the work at hand.
When I interviewed, they had not instituted the next portion of the interview, which is a Skype or web-based face to face interview with one person from HR. Generally they are looking to see what type of personality you have and if you can hold a conversation and/or build rapport before they spend the time and money flying people to a panel interview.
And the final step, if you make it through all the others, is the aforementioned panel interview. You are flown out on their dime to the location they happen to be conducting the panels in (I was shipped to Denver and placed in Colorado for work, however, other people who were in the same panel were offered positions in Nebraska and Missouri, so just because you are flown somewhere for the interview does not mean that's where you'll end up working). During the panels you interview with Division Managers and usually one director - two interviews with two sets of people that last about 45 minutes each. Most of the questions are situation based, behavioral questions, i.e. "Tell me about a time when..."
I found that during the panel interview, the round with the two division managers was much more laid back than that with the director involved - this is also because this particular director is extremely intense, even in comparison with other directors in the company.
During the panels they will also cover where you are willing to relocate to. Be honest. They will try their best to match you to a place you are willing to move to or already live if they really want you to work for the company. But I cannot stress enough - do not say you will move anywhere if you really will not. For instance, they specifically asked me if I would be willing to move to Omaha, NE during my interview. I said, no, I would not move ANYWHERE In Nebraska. One guy who was interviewing at the same time as me said he had open mobility, and he got a job offer in Omaha, NE, which he accepted reluctantly.
After the panels, if they decide to extend an offer, it is contigent upon passing a background check, MVR and drug test.