I have competed there, my dad competes there and I know several of the "regulars." I'm not going this time due to budget restrictions and the timing (summer, hay, 500 million things to do).
Always do the course walk through in the mornings and ask any questions you have about the course. They're usually quite helpful. The office staff and grounds people are extremely nice and helpful. Most of the competitors are friendly and will give advice, if asked.
Have you done any of the Mtn Trail clinics at Eugene, or will this be your first time at this type of event?