Heat up - Cool down

Is there any merit to the opinion that it's better to leave your system up and running (and therefore at a more steady temperature) than to shut it down each night? I've heard from some, that the heat up - cool down cycle is more detrimental to the long term health of the cpu (or for that matter, any component).

I'm not sure about that but I leave my computer on 24/7...

And I've read somewhere its best to keep your computer on most of the time so..

Everytime you turn it on and off.. Its like turning the flick to the bulb you turn it too much eventually it just pops out.. or at least if ya have some PSU ;p

A cold boot is a little hard on a computer. It's like a cold start with a car. However, turning it off daily should not excessively shorten the life (maybe a little, but not enough to worry about). What I would caution against is numerous off and on cycles per day. If your using the computer at 10:00 in the morning and plan on getting back on at 3:00 in the afternoon, then consider leaving it turned on. I turn my office computer off every day and my home computer off every night. Been doing that for years and years and never had a problem.

We have 4 computers in our home..

3 of them are on 24/7 while the other P 166 is on sometimes if need to see some stuff and such.