If you are training for marathon, half-Iron, or Iron distance (or comparable distances in other sports), read THIS ARTICLE NOW!.
This is the best summary of what it takes for a real age-grouper athlete to really train well for a long-distance race without sacrificing their life, their relationships, and their health to their workout schedule. It's really good!
Kudos to Endurance Nation for putting such wisdom out there, and Trifuel for posting it.