I always shut down my desktop and laptop. If I'm going out for sometime (even if it is 30 minutes) I will shut them down. Unless, of course, I'm downloading something or installing a program or doing some cleaning.
I don't like to leave the computer working when I'm not there to use it and the computer is not doing anything important. It's a waste of energy, really.
I haven't turned off my computer in a while. I only reboot them when I'm installing updates. Really, I don't want to restore my Firefox session (with 60+ tabs) every day, so I just leave it on and see how long it'll last.
I used to get impatient waiting for the system to shut down so I would leave the room and let the system shut itself off and let the monitor and other devices switch to standby mode. I only had 2gigs of RAM at the time (Windows 7-64b), I recently upgraded to 10gigs and now shut down is really fast, surprisingly so all gets shut off completely. I don't do it for the environment or the global warming hoax, but rather to keep my electricity bill as low as possible.
Sometimes I leave my pc on when I desperately need to download something through torrent(Tixati)
and when I am at work I run boinc client for WorldCommunityGrid....
But have never left it on more than a week...
I turn it off most nights. My bedroom is small if i dont turn it off the room will be hotter at night and if its a hot summer day than leaving it on combined with the 42" HDTV will make my room hot to the point where the A/C will have to be turned on... The A/C is loud so I try to avoid that scenario and thats such a waste of energy. Got a SSD so no biggie just sometimes have tasks running at night. Hibernate and sleep dont work well for me most of the time the PC will wake itself up randomly if i try to use those features.
Having 7 computers on a home network, something has to give. the server stays on 24/7 but the others go up and down. Using two dell 690s, well, in the winter I dont have to use heat when they are on and they definately go off in the summer! However, there is a lot of truth that the most stress on electronics is the inrush on power up. Generally speaking, if it's going to fail, thats when it will do it.