Daniels describes the 12 week marathon plan in the third edition of Running Formula as demanding, and it does indeed look very hard. E.g the first quality day 12 weeks out is 22 miles total divided into 4E + 8M + 1T + 6M + 1T + 2E. Some people would consider a single 10M with some warm up and down to be demanding enough.
Has anybody tried this plan? How did you fare with it?