Athlon XP 2600+ with 1024MB DDR333, running 24/7 (my PC, mild constant usage plus occasional bursts of high usage ie. games)
Athlon XP 1700+ with 256MB DDR266, running 24/7 (mum and dad's PC, zero usage a lot of the time with occasional bouts of mild usage)
Celeron-M 1.13GHz with 256MB PC133...