FWIW
1. X10 is living on borrowed time, but I bet it is here for another four or five years, or until Z-Wave prices or WiFi system prices drop to same as X10.
2. Z-Wave will lose popularity as more WiFi based systems debut.
3. Z-Wave tends to get slower as the system gets bigger.
4. Z-Wave communication is more reliable than X10.
5. Z-Wave is two way, so the controller always knows the true status of a module.
Having said that, although expensive, the Homeseer program talks X10 and Z-Wave (it can use CM15A or CM11A as an interface). Homeseer acts as a server so can be accessed through internet via remote PC, or tablet - smartphone browser. Homeseer can act as media controller, email server, etc with voice control and text to speech capabilities. Since Homeseer talks both X10 and Z-Wave you could use it as a hybrid system, migrating slowly from X10 to Z-Wave. Also Homeseer has plugins for Phillips Hue system, Lutron RA and Homeworks, Lightolier, DSC, HAI, and Gemini security systems, etc. etc. etc. I have Homeseer ver 2 and like it. Version 3 is out but their upgrade cost is outa control (pun intended).