I've been using the paid version of Training Peaks for about 6 months. I appreciate it. I've been training with a smart trainer but no power meter on my bike; I do most of my workouts on the erg, and do a long road ride on the weekend. I haven't bought a coach's training plan--I've rolled my own, which might not be ideal, but seems to work. Note: rolling your own training plan is tedious enough that it's probably a decent time/money tradeoff to just buy a canned plan that works for you. I'm just ornery.
I do find myself chasing numbers to some extent. I "cheated" today and took a rest day when I had an erg ride scheduled because my knee is kind of jacked up. In the back of my mind I was thinking about the hit that my CTL would take as a result.
Having power data is super helpful, and has really changed my whole conceptual foundation for cycling and fitness.
Golden Cheetah is worth looking at, but is confusing as hell, and uses slightly different vocabulary and calculations from TP. Also, unless I am missing something (quite possible), you can't use it to map out a training plan.