Similar to what Mike mentions above, for me it's been a disconnect at times between perceived output and actual. from a variation stand point, there have been some rides where I've ridden hard lets say 3-4 days in a row, on the last day wind is increased and perhaps my heart is feeling the affects of the previous days' efforts. My perception was that I was going hard, but then I'd look down and see that my actual wattage was way below my feel hence the comment about losing motivation. BUT, as soon as I started understanding the book and various discussions on how best to use power information I was able to get over this mental hurdle and use data for what it was intended. I'm still extremely new with it, but as has been said in this thread so far, it's been great for pacing and growth purposes, it's been very positive to turn my miles into quality miles, especially now that I'm having to do shorter rides that during the summer/fall.

Ultimately my point is that using it purely to look at the numbers is a disservice to the tool, even as a recreational rider.