Wait until you download torrents in minutes. It loses its hold on your life rather quickly :)
My PC runs 24/7.
I only restart it every 1.5 - 2 weeks for a fresh reboot.
i leave it on 24/7, also hardware are more likely to fail from constantly switching your pc on and off, cause thats when the most current flows through your components. ;)
I only shut down when I go away for a weekend or a few days. Other than that, I leave everything running with Visual Studio, Outlook and Chrome open so I can continue exactly where I stopped the night before. I only reboot over weekends if I want to log into my gaming partition which runs on Windows 7 but since I haven't done much gaming recently, my PC was up and running for 3 weeks without a reboot until I updated my graphics drivers which caused my PC to freeze up.
On and off when required - usually.
My PC is on when im at home. when im asleep or awake. I download stuff at night most of the time. I turn off the unneeded fans when im sleeping or watching movie or on the interwebs
Always on whenever at home and off when I have to go into the office.