Hi,
Yes, I have used it for about 10 years, with marginal results. Initially set it up with PC control to turn outside lights on/off automatically. I also started adding X10 outlets in the home to turn Christmas lights on/off (to avoid running all over the house each evening during the holidays.
I've found that I tend to have at least one outlet/switch go bad each year. I usually just replace it with a regular outlet.
Also, since the main controller plugs into a regular outlet, it (the signal) goes to only one side of your home circuit breaker box. I had to buy two special components that look like breakers and plug into your breaker box (taking up two precious breaker spots -- one on each trunk with a wire between them) and allow the signals to pass to the other side out the home wiring bus.
Most homes today have GFCI outlets or breakers for circuits that have a component on the home exterior (porch lights). I found that the GFCI device doesn't reliably pass the signal.
So, if you try it, I suggest to start out small and see how it works for you, as it tends to get expensive -- $10 - $15 per outlet/switch, plus the controller / breaker startup cost. Also, the PC software that I used to use was very basic. May have improved in last ten years.
There is something else coming down the pike that may effect it. I read that the FCC is supporting BPL - Broadband over power lines (
Read this if interested -- http://www.arrl.org/news/stories/2007/05/24/100/?nc=1 )
This will permit power line to also carry computer broadband service.
I don't know the details, but I would think it would have a significant potential to conflict with X10 signals. I know it is purported to cause significant interference to the radio spectrum in general (especially amateur bands).
Good luck
Michael