I'm curious about this too. I'm quieting down my PC's and I want to know what are acceptable and unacceptable figures for CPU temperature, case temperature, chipset temperature. I believe that Motherboard Monitor 5 supplies all these and I run this on both my PC's. Where can you get figures like that? Some guidelines?
I figure I'm going to remove one of my case fans in each PC and I'm making other modifications. For example, I just removed the northbridge fan from one MB. That MB didn't come with a NB fan, but the RAID version did. Come of people mounted NB fans of their own, though, and I picked up one at a computer show and put in on. I noticed it had died and removed it today.
Do you just figure you're OK as long as you're not getting crashes, lockups, etc.? Or do you want to stay under certain limits?