iYah... simple...

1) If it's for a short period of time, just put it to sleep.

2) If you're travelling or leaving the MB idle for long period of time, then shut it down.

It doesn't take that long to reboot anyways - at max, 30 secs?

Just install the smCFan Control or one of those programs. My MBP's temperature is usually below 50 Celcius.

@wei,
That's pretty sound advise but i wouldn't advise travelling and carrying the MB in sleep mode - sometimes it's better to be safe than sorry *grins*. I usually have mine switched on as I work from it and if I'm leaving the office straight for home then I usually keep it on sleep mode, otherwise I shut it off and vice versa. If I'm going for a meeting and know I won't be utilising the notebook then I'll shut it off - just in case

The boot up time on my MBP's less than 20 secs so i can live with having to wait a lil while

@kevler,
About 70:30, mostly in an airconditioned environment. Or, perhaps when it's really hot or when the temperature's soared, I don't realise it because I ain't checking it *g*

@alextakashi,
Your screen will go to sleep automatically so u don't have to worry about the room being too brightly lit when your MB is running while you're sleeping - that is unless of course you switch the default off... by default your screen will go to 'bed' too