In reply to Denni:
I've just started using a HR monitor again, not as a training aid directly, more as an addition to the gps watch it came with. One thing I noticed was that my HR, would peak at 204 on hill runs, which would make me about 16 (if the 220-age is used.) Previous HR monitors I've had all read in similar ranges. I'm reasonably fit, I've run a few fell races, marathons, an ultra and I'm training for more.
I tried setting the zones, with my max HR set at 204. I still need to stop and walk when in the lowest zone. Some of the others, fat burning for instance, are kinda soul destroying. Its more of a gentle trot, with a slow walk up any hill.
I think one thing it's good for is showing max effort. If you're slogging up hill, then you can see how much more you can push.
I spoke to the doc about my high HR. She said as everyone has different physiology, there is no set max HR that works for everyone. There are various different formula for calculating max HR, but they all have a percentage of error and come within a few beats of each other.
I'd be interested to hear first hand of any benefits for running within zones. I understand the theory, becoming more efficient at lower HR. But to have one eye on your watch, and to spend a lot of your run walking, seems to take the fun out of it.