I see hill training as a necessary "exercise". Unless you're actually running a hilly course on the race day, in which case it would pay to do long runs/tempo runs over hilly course to simulate, it is almost pointless to count mileage you run over the hill training. Assuming the schedule you're following is legitimate, I would assume the author's intention of 4~5 miles is simply a guide. Some people might have very strong legs and could handle lots of hills and simply running up and down over 5 miles is no problem; whereas for someone who's not used to running hills, 3 miles might be too much. Bear in mind you should still need to warm-up and cool-down adequately; which means you would be jogging nice and easily for at least 15 minutes before and after. Whether you want to count that as your "workout" is up to you.
Depending on where you are on the training plan (12 weeks out before the half or 4 weeks before), I wouldn't even be bothered with 5~10k pace. Hill training is a perfect resistance and technique work. No point trying to run up hard by trying to stick with your 10k pace and swing your arms and legs all over the place (you'd be teaching incorrect runnnig form). The length and the degree of the hill come in play also.
What I would personally do would be: jog 15~20 minutes nice and easily for warm-up; run up the hill "strongly" but not necessarily "fast" and jog easily down the hill and continue for 20 minutes (total)--depending on how you feel, increase the total duration up to 45 minutes or so over a period of 4~6 weeks; jog 10~15 minutes nice and easily for cool-down.
Yes, downhill running CAN be quite demanding but, depending on your strengths and weaknesses and what you're training for, as well as the length and the steepness of the hill, I would not necessarily completely avoid downhill part. It is an excellent eccentric resistance work, works particularly well for running the marathon, and leg-speed development. Of course, the hill should not be too steep and you need to work on correct runnnig technique (not landing hard on your heel, leaning backward, etc.). Perfect location would be to have a loop or a rectangle (or squair) with a steep hill of about 200~400m, nice flat area on the top that leads to s less steep hill for downhill section and another flat area for recovery jogging at the bottom.
http://This message has been edited by Nobby (edited Sep-05-2007).
I generally run by time and intensity - sometimes easy but more often in the high-end aerobic zone (75-80% heart rate reserve, comfortably hard). At some point in time, I may do them harder. I do keep track of vertical gain since that's a more useful number than distance. I also record what kind of hill(s) - slope and size - or whether it's generally rolling (steep or gentle). They all have a role in my training.