I always do after I’m finished using it, for overnight or what have you. Yet I just read someone who says he never does so, except if he’s not using it for long periods. Apparently, the factors that used to make this not such a good idea no longer exist with modern computers/OSes.
How often do you shut down your computer, as opposed to putting it to sleep? Does OS or desktop v. laptop make a difference?
I use windows 7 on my desktop and windows XP on my laptop. I turn each fully off a few times a week. Forced restarts for new program installations or OS updates are much more frequent though.
I think a reluctance to restart her computer was one of the major issues with my girlfriend’s machine. She fell way behind on updates.
I only restart when I need to for updates or when I’m going to be away from it for more than a day. I use a laptop with Windows XP. No problems so far.
I have five computers (one a laptop) that only get turned off when they need it (restarts after updates, that kind of thing), and one that only gets turned on when I need to use it.
Every month or two. I usually put it on sleep mode when it’s not in use. Windows XP desktop.
Mac OS X 10.4 on a PowerBook. I use it daily, for at least six hours per day. It automatically goes to sleep after an hour of inactivity. I only shut it down when I’m taking it out of the house, and I only restart it when it asks me to or when I’m troubleshooting a specific program or hardware. I’ve experienced no problems at all.
Every night.
One of my desktops stays off all the time because it’s garbage. The iMac only gets turned on when I need it for work, and then gets turned off when I’m done.
My circa-1999 laptop goes into sleep mode every night when I close the lid, but I only reboot it when the video processor futzes out on me.
My TV desktop stays on all the time unless I am away or I reboot it for an update (or in the rare case that something goes wrong with it).
Same goes for my office desktop.
I can’t bear to count the hours I’d lose over a lifetime waiting for a computer to boot up every time I needed to use it. My time is precious! 
We’re required to shut down every evening at work. At home I do so whenever I’m finished using it.
Every night. The light keeps me awake otherwise.
My G5 Mac goes to sleep if I’m off it for 30 minutes. The only times I actually shut down is when I go out of town or during a severe thunderstorm.
My G4 is usually down, unless I need to do things on two desktops at once.
My MacBook is usually down, except for vacations and monthly meetings.
On the machine I’m using right now (MacBook Pro):
20:31 up 42 days, 21:41, 11 users, load averages: 0.67 0.57 0.43
I just make it sleep when I am not using it, reboot only for software updates. I don’t remember the last time I actually shut it off. Only if I’m opening it up to do something with the hardware, or if I’m not going to be using it for a long period of time (e.g. a trip I’m not taking it on).
About every 7 to 10 days to do updates or otherwise as needed but still not very often. Windows Vista desktop.
One I turn off every time it’s not in use, partly because it has a noisy fan, partly because it’s so rarely used.
The other stays on all the time, just to prevent the hassle of booting it to start; if I want to use it, any time of day or night, it’s instantly accessible. Though it has to reboot for the XP Updates and the occasional app install.
Every night.
I do not want the thing burning electricity all night. Bad for my wallet and bad for the environment.
Each night. I used to sometimes put it to sleep instead of shutting it down but occasionally it would start up by itself for reasons unknown and I’d be woken up by the light and whirring. I don’t need anything else interfering with my [lack of ] sleep, so I shut it down now.
Once or twice in a blue moon. Unfortunately, my janky vista laptop slows to a crawl if it goes to screen saver so I’m forced to decide if I want to restart in order to watch youtube AND chat on facebook. I don’t like restarting because one time when I restarted, my computer made awful noises and told me the hard drive was broken so I took it out and put it back in again, a procedure I am given to understand is called reseating the hard drive and it worked. I live in fear, however, that one day I will turn it off and be unable to turn it back on. Although I think what the moral here really is is buy a new hard drive.
My computer is usually on about four hours per day. I go on-line for about two hours in the early morning and perhaps an hour or two in the evening other than that it will be turned off.
Only when I’m going away.