Thanks for all the great information!
Hmm so there's no PL -> RF forwarding type device? I was trying to figure out if it was feasible to have everything two-way communicative, so that no matter how you toggled something like a lightswitch (remote--RF->TW751--PL->switch, PCusb-to-PL -> switch, actually pushing the button on the switch) all your controllers (web interfaces on PC or mobile devices, mobile apps like x10 commander, RF remote control) would be seeing the correct state.
I guess I was thinking I mainly want a web interface to control all my x10 gadgets. So for the shortterm, installing some x10 controller server software on my windows machine, but in the long run, putting together a (perhaps) microATX, 100Watt-ish computer running a light flavor of Linux to do little more than run some x10 controller server software. I really like the idea of a web interface, because that means you can access it on anything with a web browser (e.g. any pc, virtually any mobile device, someone else's anything without having to install extra software/apps). I suppose I could give up the RF remote, since I do have a browser-capable mobile device (iPhone).
I was also considering rolling my own web back & frontends (I have skills to this end), assuming I was able to figure out how to make the device calls (no skills on this one) to the transceiver connected to a pc.
Somebody compiled a massive list of related links,
http://linuxha.com/My conclusion so far is that most x10 devices (by a wide margin) don't respond to any sort of status queries (correct me if that's not true). So the work/cost to set up such a status-reporting capable system goes up much more than it may be worth.
Also I can get a CM19 + TM751 for less than $20 after all costs. I can get the CM15 for no less than ~$43. For my goals (complete bidirectional PC integration), is that extra cost really worth it? It's not THAT much money to me, but I'm just wondering.
Thanks