I have known people who used it. Its neat to play with but not the most robust system. It transmits signals to each reciver over the power lines and causes some interference with other devices as well as being susecptable to interference its self. There are better systems out there (search for home automation).

Also on a site note, Yahoo and X10 started the whole internet browser popup ad game which put them on a never do business with list of my own with other spammers/telemarketers.