Our house computer is a modified 586 running linux. It has 2 ISA interface boards, talking to a group of custom boards. It runs a pile of software, most of which is too krufty to distribute(although other people seem to want to distribute their home automation software).
The hard disk automatically winds down after a period of inactivity using the hdparm utility. The CPU turbo switch has been set to switch between 200MHz and 1MHz, it is connected to the ISA bus which allows the software to run the machine at a low frequency(hence lower power, longer life) until something CPU intensive(mainly compiles) pulls it to fast mode. I should really tidy this up and distribute it - it is probably useful in laptops (ACPI already does this, so maybe I should build a driver for that or something).