Of course the best way to introduce cats to harnesses is when they're tiny.
The harness impacts the cat. We started my cat on the smallest strap-style harness you can get at any pet store. It became the signal that we were going outside to tackle the world together. To this day, little buddy (now 4 years old) purrs whenever we start getting him dressed. Even though it's not his favorite thing to wear, he knows we're going on a hunt.
In his early adolescence we transitioned to the standard, velcro-only
walking jacket from Hyendry.com. It's much more comfortable for him, looks great on him, and is now his default harness. It's still lightweight and doesn't inhibit him much, but I believe the fact that this 'walking jacket' is larger and covers his back a little (as opposed to the strap only harness) is a constant reminder that I'm present and in control.
I also picked up a second harness from Hyendry, this one with the "double lock" feature. which is a thick, nylon adjustable 'belt' sewn into the harness (as seen in this
photo). When he wears this harness, he feels like he's wearing a straight jacket. As long as the straps are adjusted right, he can move around no problem, but he knows he's wearing something heavier, senses the security of it, and he is more constrained especially the tighter the straps are. Sometimes I use this harness when we're in a new place, when there are going to be lots of distractions, or if I just want added peace of mind.