i don't think friel's ideas are crap, i just think people need to tailor their training plans to fit there hours. Obviously if you ride 10 hours a week w/ your longest ride being 2 hours, then z3/z4 are necessary! If you ride say 15-20 hours a week, its a whole different ball game (not just one 15-20 hour week, but three in a row), you would burn out quickly on a big diet of tempo, or t least higher end tempo.