I'd say that I've generally managed to adopt it as a habit; if I have failed to get enough exercise with this, it's because I have too often gotten wimpy exercise (like a ten-minute walk each way to buy lunch) instead of something more solid.
This past week has been low-exercise, though, largely due to sickness.
Thursday night, I felt tired (this was probably a precursor of sickness) and decided that I'd rather lie on the couch and read than exercise in order to play WoW.
Friday, we drove up to Cook Forest. I did get a bit of exercise and WoW before going up.
Saturday, we mostly drove around and went to shops in Cook Forest; I considered trying to get a brief hike in, but at every time when we had some free time, I chose to nap or sleep instead.
Sunday, I still felt sick, but we did manage an hour's hike in Cook Forest.
Monday and Tuesday, I felt sick enough to stay home from work. I played WoW anyway, and decided that I could amend my rule to say that if I felt sick enough to stay home from work, that exempted me from requiring exercise.
Wednesday, though, was my worst contravention of my rule. I felt well enough to go to work, but not so well that I wanted to take a long walk to get lunch.
I had ideas of getting some sort of feeble walk in during the afternoon or evening, but much of the evening was taken up with celebrations for Lori's father's birthday.
I got home just at 9:30, and I knew that there was a Karazhan raid group gathered at the instance portal waiting for me to log on. So I gave that priority over my daily exercise.
The days are growing cooler--rain and snow will soon complicate my exercise habits. I hope that I manage to maintain this habit through the winter.