I can already see why MAF training is popular with those who now swear by it. Firstly, it makes running fun again in that you have something to do other than beat on your legs (and heart). These slow miles "fly by" because you're paying close attention to your heart rate.
The next interesting thing was that I felt 'fat burn" in my legs. I don't usually feel burn in my legs unless I've taken time off due to illness or even changing to cycling. To have felt that during a slow run tells me that my body is using a different source of energy.
And it bears repeating that it is very nice to not be totally knackered at the end of a run. VERY