I've been toying with the idea of ditching my PM. I've been using it steadily for about five years now, and it has helped me a ton. In fact, I found it so useful, I bought a Quarq for my wife.
But I have not been using the PM or HR or a computer over the last three months or so. That is mostly due to the fact that since I tweaked my knee, I haven't been putting much effort into my rides so I saw no reason to track power.
After substantially changing my training plan last year and upping my total time on the bike, I am getting a little burned out. I am thinking that by riding with out the PM for a little while that will allow me to just enjoy riding without worrying about effort or HR or mph or anything else.