Running

Does anyone in here have any experience with LD ultra running. I've been off running (and since I don't have a bike with me at the moment that also means all sport) for a month to let my knees recover and I'm getting twitchy. I'm thinking about entering this race but I'm a little concerned about injury prevention and super long miles.

Ive done the MDS and the Al Andalus Ultra (twice) and I heartily recommend them. I find ultras good because the pace comes down as the distance increases, so it becomes more of a test of will. Everyone knows they are going to hurt, but it becomes a test of your resistance to pain.
I'm not fast, but even at the back of the pack you get an amazing group spirit. Once you've run 50 miles, everyone running with you seems to be your best mate.
Be prepared to lose toenails though, ultra-runners feet are nasty!