my old Pentium 4 1.6ghz ran the 24/7 shift starting jan 2005 when we got dsl, i left it sa pinas last august and still works, the only time it was off was then there was a blackout, my power bill ran P2000 a month(i had 1 tv, 1 personal ref, ps2, 1 electric fan, and the celfone/psp charge)
now im using a 2003 compaq presiario 2ghz runnng 24/7 here in california an havent had any problems