I’ve spent tonight partially building a new file/print/mail/dns server for home, on somewhat unconventional hardware: an old, written-off laptop (the screen was broken). With a bit more RAM and a new hard disk (I’ll use something like Ghost to transfer the OS), it will give me a low power server for less than a mini-ITX with a built-in UPS (so my UPS can just run the network gear). As laptops have good ACPI support too, it can be shut down from the power button, and will go idle when not in use. Obviously, performance won’t be that high, but so long as it can cope with Spamassassin, that will be fine.