Ahh.. that's all good to know, thanks guys.

I did notice one in kit form at our local shop, but there was
too little tech info for me to decide whether or not it would
be easily usable on Linux.

It is perhaps a tad expensive and large for one-of uses,
but fun to play with otherwise.

Along the same vein, here is an electronic replacement
for the relay board I used.

And here is a nice, cheap real-world relay interface kit
that works over serial (or USB if one adds a USB-serial converter).

EDIT: And, ooooh.. remote control of stuff via the telephone,
and reasonably priced, too. I can't think of how many times
I've wanted something like this, to reset or power-on a box
while I've been far far away..