Ok this is very pure and simple to answer so I didn't read the other posts lol sorry if I'm repeating something someone else has said.
NOO 24/5 is not bad for your cpu, as long as the cpu was not bad to start with. It's better to run for longer periods of times, since the cpu doesn't expand and contract as much. It's bad for your PSU, HDD, and fans, since they are rated to spin for a certain # of hours (not sure about the HDD part...). If you still worry, then simply underclock the poo out of your entire system when leaving it on with AMD Overdrive; lower NB, HT, PCI, Multi, everything. Multi should auto underclock the cpu when idling if you have cool and quiet enabled.
So basically, you may have to replace the fans and PSU in like 5 years of running 24/7, that's all ^.^ Wait, I forgot to mention that running it 24/5 means your computer faces lightning storms, power outages, and all that stuff. Plug it in a UPS with surge protection and power conditioning, if you care so much about your pc. That's probably the best you can do for it. Or, buy an Intel Atom lol. But seriously, you're gonna have 1% load on cpu, so who in their right mind buys a $50 hsf to cool an idling cpu?