I haven't heard of Mars Direct, but from reading the link you gave me it sounds like a plan to start automated fuel production plants on mars to make fuel for trips back to earth. It requires the transportation of a small nuclear power-plant to mars as well as hydrogen to synthesize methane from the carbon dioxide already in the atmosphere. Off the bat I would say that hydrogen would be a pain to transport to mars (hydrogen has a high energy density by weight but not by volume) but don't know much else to think about the project.