Even more than just 'machines', think chips. Now that the peripheral architecture has shifted to USB and PCIe/x is much more decoupled from the creaky 8086 bus that drove 'ISA', we're seeing single-chip PC's with ARMs and other more RISC-y CPU architectures where you have gobs of memory and FLASH on one chip. Once you get away from interconnect, disk drives, and multi-part packaging, the price of computers goes way down. I've seen single-chippers with 256M of RAM and 256M of FLASH, gigabit ethernet and multiple USBs, and they're going to _retail_ for a hundred bucks or less (current models here). Oh, yeah, and they don't need fans, either! What's your programming going to look like when you have a stack of them in a box? Or, even more so, when your _wall_ is covered with them?

We've already seen the beginnings of this with modern cars. Now that serial data busses like CAN are common, virtually every idiot light in a car has its own little CPU. The same thing will happen with houses, although it won't be ubiquitous. The thing to realize is that once you put _any_ silicon in a widget, you can add a CPU for no additional cost. Once the bugs are out of power line networking (or, at least, the standardization of a minimal bug implementation), you will see _everything_ having connected processing power. The truth of things, these days, is that having an ARM and gobs of memory with a multi-hundred-megahertz clock costs very little more than an 8051 running at 11.059 MHz. And, once the English work on static asynchronous CPU designs hits production, power usage will cease to be as big an issue or cost factor. Likewise, shrinking geometries lead to lower voltage swings. The only remaining barriers to ubiquitous computing will be the toxicity of the semiconductors being doped, but economy of scale will solve that, too. Even without considering the coming of photonic computing as a replacement for semiconductors, I can see a not-too-distant future where every manufatured thing from structural framing to toys has a networked wireless CPU in it, even if the thing itself has nothing needing control. This fabric of CPUs will enable any house to have a plethora of active agents in residence.

Why? Ask rather, why not?