Thanks kjpetrie, that answers my question. Looks as if lower wattage chipsets are imminent and solid state drives are dropping in price. Looks as if the parts to build an ok system would cost say £200ish (board, 1GB ram, case, SSD drive to reduce power consumption) Install system via a USB "live" drive.
OldJimbo to answer your point these systems look like fun. In due course I might set one up facing the world and see how long it lasts. Maybe apache, ftp, ssh and whatever. Low power means low operating cost, same as a 40 watt light bulb. Will run PCLOS so nice and easy.