I have some issues with the new i5 ivy bridge CPU installed on MSI G43 with 650W PSU. So my main problem is when the CPU goes in idle mode the usage goes to 100% and temp is hitting nearly 80C. That's a bit strange because when I'm pushing the CPU the max temp is no more than 65C. It is very annoying to watch something which does not require constant keyboard or mouse usage as the CPU goes in idle mode and everything starts lagging.
check to see that when the mb goes to sleep the fans are not stopping. also check the sleep state in the mb bios. see if it self for default settings. sometime you have to adjust those so windows will put the cpu into a sleep state.