Hopefully I'll be doing it again this coming year.
My advice is;
If you are fit; make sure you get on the start line early as you will get held up by the slower riders as soon as you hit the first climb.
The first few miles are neutralised behind a police car (how cool is that!) but watch out for overlapping wheels as I saw a beaut of a crash last year (and its ensuing near fight!).
Expect extreme weather as the last edition was baking (and I mean baking) hot but the previous was run in hailstones.
Don't underestimate the event; if you are doing the 100k it's very tough with climb after climb, and much of it around ploughed fields or on grass.
If it's dry then it's very bumpy but if it's wet the ground can be very energy sapping.
I've done it on a mountain bike before but used my cyclocross bike last time. I'd say that if it's dry then an mtb is better to absorb the shocks but that a crosser is better in the wet.
Finding your way can be a little tricky too. I just followed everyone else last time and didn't go wrong once. My mate meticulously followed his map and went wrong twice - tortoise and the hare - we finished together.
There are some pictures on the YOGi Cycling website aslo you can see me suffering at
http://www.davidbirkinphotography.com/photographs/20070415a/14-30---14-59/20070415AA1624.htm