I have done one 24 hour run (the obvious one!). It is the GPS thing which sounds seriously crap to me. Yes, I can well understand that after 80 miles oor so your brain is mush and you don't want to navigate, and I can't see anything wrong with flagging such a course at the relavent junctions etc. However I bet that these guys haven't asked a single land owner for permission, hence the use of public rights of way and insistence on GPS, as they can't mark the route.