I just started cycling last December and bought a Power Tap in June/July. The first thing that I noticed was how I really wasn't trying as hard as I thought I was. The Power Tap clearly lets you know when you are not putting out the effort that you should/could be. I think I was taking too many breaks during my interval work & not even realizing that I was taking the breaks. In the end the Power Tap did increase my rate of progress.

I also have the books mentioned above and try to use the Power Tap to maximize the benefit.

Finally, the Power Tap has helped me on climbs at events. I now know what wattage I should be able to hold over a certain xx minute climb so I don't start out too hard or too soft. I don't hear people talk about this aspect of the power meter very often, but it has helped me.