Again like anyone here has learned: If it does not lock up, the temp don't matta, unless you overclock.
That's generally true, but not <i>entirely</i> true.
Electronics in general dislike heat. Not because it causes them to lock up, but because excess heat shortens their lifespan. So if you plan on keeping your PC for 5 to 10 years (believe it or not, some people do) then keeping the heat as low as possible, as well as keeping the voltages regulated as steadily as possible and keeping the system free of dust, can all be very important steps to prolonging the life of your PC.
Of course, if you plan on getting a new PC in 3 years or less, then who cares how hot it is so long as it isn't crashing.
<A HREF="http://www.nuklearpower.com/comic/171.htm" target="_new">The corpse you find may be your own.</A> - Black Mage