Operational lifespan of a CPU is reduced with overclocking, because of the higher temps that result.
But assuming you don't intend to keep your CPU for more than ten years, you have nothing to worry about. Modern CPUs have multi-decade lifespans. Even if you were to chop that in half, it would last long into obsolescence.
Assuming you keep the temperature under control and keep the voltage at or below the recommended maximum voltage, an overclocked CPU should last long past its useful lifespan.
As an example, I have a launch E6600 (2.4GHz C2D, circa August 2006) that has been overclocked from day one.
It is normally ran at 3.2GHz 1.35v but is taken to 3.6GHz 1.55v when the woman is editing videos or gaming.
After running nearly 5 years under a constant overcock I have had no issues with it and fully expect this CPU to outlast my last LGA775 motherboard.
Basically, have fun overclocking your chip and don't worry about its lifespan!
Wow. Most people have problems being under a constant overcock. Way to stick with it...
I very rarely encounter overclock related problems, and when I do they are almost always lacvk of voltage/stability related. Not sure who you have been talking to, but here the overclocks are standard.
You can hit the Amd or Intel web site and check your cpu's max stats then oc. I have been running a 2.66 woffdale chip at 3.2 for a while. If your mobo has downloadable software that will oc. automaticly use it as a guide.