It's funny that this thread came up. I decided this summer to try MAF training.
Let me say first that there are only small differences between what Maffetone advocates and what Lydiard, and, especially, Van Aaken recommended. Almost 30 years ago, I happened upon a copy of Van Aaken's book, read it, was intrigued, bought a hrm (EVA advocated training at 120-130 bpm) and, within a year had improved markedly. (Like 2:50 to 2:35 in the marathon) simply by slowing down and running more.
Over the years I continued to train (when I've trained....) at that heart rate. The problem is that, as I've aged and detrained it's become the case, I think, that 120-130 is no longer the appropriate range. This was brought home to me when my son finally convinced me to run a race with him - a road mile. I wore my hrm as much because I forgot to take it off and what I saw from the data from the race was eye opening. I ran that race as hard as I could and my hr never rose above 170. It occurred to me that, to put it simply, I'm old and the days when my max was around 190-200 are gone.
I kind of remembered something about MAF training and its similarity to EVA and googled it. One difference is that instead of one hr for everyone that EVA advocated (or at least in my interpretation) Maffetone takes into account the effects of aging. So, now I've switched to 112-122. At first, I had to walk just about the entire time, but, over a few weeks, I'm now up to running quite a bit of that. I know that, eventually, I'll be able to run all of it and, then at an OK pace. This happened when I'd run at 120-130. About 15 years ago, I was coming back from an injury and started at 8 min/km! Over the course of just 4 months, my pace at that same hr fell to 4:45. There was a proportional drop in my LT runs and, after those 4 months, I was racing nearly as fast as I ever had. This stuff works.
It does require patience and a lack of ego. If you're the sort of runner that is bothered by people seeing you run slowly, then this is not for you. If you care about performance and health, though, I, for one, can recommend it.