Actually I'm the person behind the framistats effort. I posted about the X10 awhile back, maybe 2 months ago when I actually took some action. The idea has been tossed around and even worked on somewhat in 2003 (see: X10 appliance timer, although this version interfaced directly to a wireless keyfob).
I've been toying with the idea of using X10 as I saw arduino has a page about it. I picked up two PL513 power-line interfaces at a cost of about $5 each. These devices have 4 wires and allow a microcontroller to put X10 commands on the power line. My main concern with this option is reliability, which can be affected by line noise and/or faulty house wiring, among other things.
As for the making money part, the lack of certifications as well as, no money for patents, keeps me from mass production. Well, also I'm pretty lazy and unmotivated lately, and neck-deep in medical problems. Still, there is a certain niche market which I've been targeting (albeit half-asses). It is actually the hobby which prompted me to make these devices. I'd love to produce such a thing but I hold myself back for being scared of the technicalities. This is partly why I've leaned towards open-source, and perhaps just selling my PC software. Plus I like to contribute to the open-source world, really.
Every once in awhile I'll see someone's project trying to accomplish the same task, and I have even collaborated with people trying to do this and make a commercial product from it. But more times than not, the whole thing either turns out to be more than they can handle, or they lose interest in it (as is the case with me, often).
In five years of tinkering with environmental monitoring and control, I have only seen one product tailored to the hobbyist, within the budget of a hobbyist. That is growtronix, however I tend not to like it because a) the high price, b) the fact that if the computer loses power or the software crashes, nothing works. And c) they're competition, naturally. I hear that growtronix is a one-man operation, and it works like this: You pay them, then they order the parts and build it, and send you your system when they're done in about 3-6 weeks.
The one innovative feature of theirs is the use of telephone cable as interconnects (RJ11). Their various sensors use some standard in automation (CAM?) so that could have its benefits over something completely proprietary; the interconnects allow expandability. But OTOH, using X10 in a device like this would offer up to 255 different devices to be switched.
Anyways, I wanted to put all that out there for anyone who stumbles upon this thread and would like more information. If you would like I can dig up more notes and links to other's similar projects for your reference - in five year's time I've amassed quite a collection and have considered environment automation from almost every angle conceivable 
