I had one cat that was leash trained, but my current cat isn't. My previous cat (Daria) was very dominant and a little aggressive, and loved being outdoors. I would take her across the street so that she could play in the tall grass in front of the high school. She occasionally got mad at me for not letting her chase little dogs, but she loved it. We didnt go for a traditional walk; it was more like letting her go outside to hide and jump around in the grass.
My current cat, however is not built for this type of activity. Jane freaks out any time she has to leave the house, even for a few seconds. She whines and cries, and if its a long journey, she will eventually find somewhere to sit and shake (the opposite of Daria, who was mesmerized by semi trucks). Jane is a cat with a delicate disposition. She also walks around like she's dying whenever she's put in a harness. She pretends like she can't stand up straight any time she sees you're watching her. So no walkies for Jane...