I leave 2 on, turn others off, leave on my linux firewall/router- if I dont then no other pc's can get online, also leave on the 2k system- this goes off and theres no printer, theres also a lot of shared stuff on this box, my main one goes off though, dunno why really, the kids also goes off when not in use. LOL, I often check mail in the morning before work, then leave the pc on all day, few hours on it at night and then off- bit pointless really.
Next time you wave - use all your fingers