Just to add to the PLCBUS discussion. I pretty much have all my house lights using it now. I've only bought one crystal wall switch, and yes, it was a bit of a pain having to patch up half the existing wall switch hole to make it fit.
I also tried using standard clipsal or hpm (can't recall which) momentary switches for the lights, but I didn't really like the stiff feel of them. You had to give them a good push to get them to work. So I've gone for the simtone momentary wall switches. Sadly, the square size means I'm back to patching and painting the wall switches to make them fit, but they have a much nicer feel and look in my opinion.
My biggest problem is that the ripple control signal that is sent out by the power company to control tariffs plays havoc with my dimmed lights. They flicker badly for about 10 seconds on the hour, almost every hour. Not sure how to fix that. I'm going to see if the Megaman DimmERable (not to be confused with the dimmable range) compact fluorescent lights are any better...as soon as they make it to Australia and assuming they work with the PLCBUS dimmers.