It's clear from the problems people have that lots of the people doing automation are in what I think of as "new" houses, i.e. much of the wiring is already grounded, and the walls are sheetrock instead of plaster I've never lived in a house that new myself.
This is probably obvious to anybody comfortable messing with house wiring, but when you have an old-style switch-loop on a ceiling fixture (hot and neutral to to the ceiling box, hot is connected to a wire going down to the wall box with the switch, switched hot comes back from the wall box with the switch and is connected to the ceiling fixture, and neutral is connected just to the ceiling fixture), it's quite easy to convert it so that you have a mechanical switch in the wall that talks to a light module in the ceiling box which controls the actual light.
There's another way, not quite as obvious, that's also useful; Re-purpose the loop wiring to be a normal feed (hot and neutral) down to the box, and wire the light to just be controlled by a module in the ceiling box. Now you don't have any direct button to control the module, but you DO have a wall box with hot and neutral available; you can then install anything, but specifically a scene controller (or a zwave wall switch with no hard-wired load, used as a limited scene controller).
The more I work with this stuff the more I love the in-box modules! They provide so many really interesting possibilities.