The first phase of the process is a phone interview, which is easy and requires no preparation (they just verify resume info). Before the phone interview you also have to do an online personality test (also easy).
The next step is they fly you over to Madison, which is a surprisingly lovely city. You're set up in a nice hotel and you can opt to have a free dinner with an Epic employee that night, which I did. This is where things start to go down hill as all the trappings of a fine-tuned, mass-interviewing apparatus become increasingly apparent. You don't get a one-on-one dinner. Instead, along come 5 or 6 other people, all interviewing for your same position the next day (that's okay though...Epic is such a large company that at any given time they've got to be hiring for multiple vacancies...so no worries yet). I had a blast at this dinner, really talking and getting to know my fellow interviewees. The Epic employee mentioned that only about 0.1% of applicants are hired at Epic, but that number sounded so bizarre as to not be plausible. I dismissed it.
The next day my cab driver warned me that I "have a lot of competition," saying that for the past 3 years Epic has been interviewing 10-12 applicants per day, every working day of the year. I was not too worried by this, since afterall I love a challenge. The whole interview process consisted of 6 hours of a mix between them providing meinformation about the company/their software/the project management role, interspersed with verbal, math, and programming assessments, a project management interview/assessment (they give you a PM scenario and you have to identify the biggest problems and how you would address these problems), a 10-minutes presentation that you give on the topic of your choice, and a 1 on 1 interview with HR (this came last, and after getting up at 5am and going for 6 hours straight, it was difficult for me to answer her questions). During part of your day you're with a huge group of other interviewees, and many of the staff that speak to you seem bored (as if they've done this a thousand times).
Overall, the whole experience seemed to be a waste of time giving the poor odds of actually being hired. If you do go on this interview I suggest giving it your all, but not investing too much of yourself in your prospect of being hired.