It will boot Debian Etch (aka stable) from a read only CF card, while all downloads and backups are stored on an external SATA drive which I can switch on and off from the commandline (still work in progress though).
Read it here
Recently I bought myself a Thintune Micro-PC after my old download and backup server crashed (RIP rammelbak). I was searching for a low cost replacement which did not make as much noise as Rammelbak (that was the hostname of the old server) and was not as power hungry. All of a sudden there was an auction on samenkopen.net and I managed to get one for 50 EUR. This system is completely fanless, and boots from a CF (compact flash) card which is put in a CF-To-IDE converter.