Because I didn't start keeping a daily journal or recording daily vital signs until the start of Phase Two, I'll try my best to sum up my experiences with Phase One.
As you might recall, Phase One is the easiest, and simply involves adding three 20-minute naps to your schedule, spaced equally apart as much as possible (again, following the standard Everyman approach). My experience with this was mainly an exercise in consistency, and in finding what little changes I need to make to reliably incorporate the naps. In this regard, I think the simple addition of naps as a first step more than proves it's worth. Unless you are especially well-organized/prescient, you are bound to discover inefficiencies or sub-optimal timing for those three naps, and I'd much rather take time to optimize my routine before I start adding the stress of a gradually decreasing amount of sleep (in Phase Two). For myself, this involved some experimentation with naps times until I was really happy with the schedule. After I settled on one, I haven't had to make much changes to ever since!
As for the naps themselves, I will say that I often found it difficult to reliably get to sleep each time. This was mainly due, I believe, to the fact that I wasn't really sleep deprived, since my core was still sitting at eight hours. Oftentimes, I would lie there awake, not doing much except trying to enjoy the peace and quiet for the 20 minutes. Eventually, my body got used to notion of having a reliable nap time, and I occasionally began to fall asleep lightly or dream a small amount.
<Work in progress>