Should I leave my PC on 24/7?

There are two differing opinions on this.
The Turn it off type feels that He or She is saving energy and the operating life of their components.
The leave it on type thinks that the thermal consequences of constantly heating and cooling components across their operating range. By leaving their machine on, the internal temperature of the parts remains constant thereby reducing the possibility of lubrication variances in fan bearings and spindle bearings in hard drives.
This is the Conclusion I've come to after years of servicing the leave on and turn off PC's…
If you use you PC daily, leave it on and in the Power Options icon in the Control Panel set your Monitor to turn off after 30min, (mouse movement will wake it up). In the same Power Options icon you will find a tab called Hibernate. Click on the Hibernation box. If it won't stay checked, your PC may not support it. Also, some Backup Battery Power software may have their own settings. If the check remains, click apply and OK and test it by going to shutdown the PC. Select Hibernation which should now be one of the choices with restart, shutdown, hibernate, etc.. If it hibernates it will shut off. When you turn it on, it will execute the hibernation file and you'll be at the desktop in about 20 seconds with everything loaded. You can go to Power Options as instructed above and set your PC to hibernate after a couple of hours if you chose to. You must do a regular restart if you put in any Windows updates or new programs. If your business PC sits unused over the weekend, turn it off. In general if you are not planning on using your PC in the next 24 hours, give it a rest. Fans and drives usually fail after a PC has been restarted. The plain bushings used in 85% of the PC fans are a major part of the problem. By asking for the optional Cooler Master & Enermax Cooling fans, you will have one less thing to concern yourself with as I have never seen one fail. I believe hard drives have peaked as far as reliability. What I mean by that is with prices dropping rapidly, I don't expect more then 5 years of daily usage before copying your data to a new drive. As profit margins thin, these companies may be cutting back on quality control. No way around that as you get what you pay for. One more reason to install that Maxtor One Touch II backup external hard drive.