Well, I have 3 systems. My main system is a Celly 566@850MHz on an Abit BH6 in a highly fan cooled Addtronics 6896A case, and it hovers around 33-35C in the day, and down to 27C when I turn on my aircon.
My HTPC is an Athlon Tbird 1.4GHz on an ECS K7S5A in a default cooled Enlight 7237 in a stuffy rack with not much ventilation. Case temps are normally in the high 30s.
My dad's PC is an Athlon XP 1800+ on an ECS K7VTA rev3.1 in an "iCute" Taiwanese brand mid tower case(these are popular over here) and runs above 40C with the case open. However, I don't think that is entirely accurate as there's no reason why it should be that hot. I guess it might be the sensor.
How come there's no choice for >40C?