I leave mine up 24/7 but that's what I do... and we have had this topic before and it turned into a flame war cause all the tree huggers, er... I'm sorry, not politically correct... caring people of this world though we were going to burn down every tree, drain every lake, and tear up to Ozone for leaving our computers on all the time...
I for one use all 3 of mine for either tech forums folding, or SETI@home.