IMO a lot of ultra running is done with your head. If you can keep positive you can keep going. I run a lot slower in an ultra than a road marathon, so hitting the wall has not been an issue. Battered feet from off road running is my main problem (as well as convincing myself that I can't make...
What event are you looking at LB?
I did http://www.saltmarsh75.co.uk/ at the weekend.
My training is largely the same as Marathon training, with my midweek runs being 8 miles (sometimes I'll run the 13 miles home from work). Also the addition of a a couple of weekends where I'll do back to...