Thanks for the link. It looks very interesting, but I already started Couch-to-5K and I want to see it through. The first six weeks consist of interval training, like the simplefit plan. I chose it because it has a clear goal (running 5K or thirty continuous minutes) and only takes two months. The other factor is that I'm trying to get myself to enjoy running, and from what I've read, Couch-to-5K works well for that.
You talk about reducing your mile time, but at the moment I doubt I can run even half a mile without stopping to catch my breath. Maybe once I've built up my endurance and finished this plan I will consider the simplefit running program or something similar.