In reply to b_fillmore: I did the 100 this year - as a survivor rather than contender - finished 100th in 37:08. I'm not going back next year, trying to get a place in UTMB instead.
Presuming you're in the aiming to finish rather than win camp the lessons I've taken from this year are:
If possible recce the course to the extent that map and roadbook are redundant. The official recce days are said to be excellent but I never went on one. You don't need nav sapping your time and morale on the second night out
At as early a stage as possible identify what (reasonably cushioned) shoes and pack and hydration system (and poles if you're so inclined) suit you and use them on your long training runs
Do some starvation runs to get the fat burning trained and some stuffing your face with "proper" food runs to get accustomed to that
Do some overnight runs if you're not used to them
Don't neglect strength and core work as you get obsessed with building up the miles
Hope you enjoy the journey to the starting line, it does have a tendency to take over your life! It's an amazing event - I'm already rather regretting not doing it again. I'm very pleased with my T shirt
P