I did it last year too- was in the winning (only?) team of 4 girls. We had a blast! Apparently the course is better than last year, and last year it was pretty good. It wasn't too technical but I thought it was interesting enough to make you want to go out again, and again, and again... Unlike 24 hr events south of the border, there was no cyling round fields- this was proper mtb territory!
If it is your first event, prepare to be more tired than you have ever been on a bike. Take all the cycling clothes that you have (within reason- you can safely leave the summer stuff behind) and be prepared for every weather situation- it is Scotland after all. You can't beat getting into warm dry clothes when you finish a wet lap. I also remember from last year that it was really cold at night, despite wearing everything I had, so take loads of warm clothes. Also remember that it will be dark from around 9(?) until around 7(?) so you will need plenty batteries.
You have to eat lots, drink lots of water (or better still, energy drink) and rest when you can. It is certain that you will take loads of food and not feel like any of it, especially during the night when you don't normally eat but you have to force yourself.
There are loads of high points of 24 hour races, including the dawn lap which can be spectacular if the weather is good. There is always a good vibe at the No Fuss events as they tend to be less competitive than, for example, SITS. No-one trying to force you off the track for a 26th place in the teams of 4!
I'm hoping to find another girl to be the other half of a pair. don't fancy it solo...