Yep, Athlons have been warm. The thing people forget is, they're rated to *take* the heat they produce. As long as it's kept within the range specified in the datasheets, you can expect it to tick away as long as anything else, or until your Taiwanese capacitors explode.
The processor might be able to take it, but what about every other component in the system?
1 - electrical conductivity improves if components are cold. Equals faster.
2 - if you switch the computer off at night, all the components cool down, and with today's machines that can mean a reduction in temp by about 20 degrees C. Heating up and cooling down something repetitively is a great way to damage it, killing it far more dramatically than if it was on all the time.
3 - Hard disks die much quicker if they're running hotter. They may be rated to work at {insert high temperature here}, but the specs don't show you how that effects the MTBF (mean time before failure). Personally I care far more about the data than most of the other components in my system.