Increased voltage to OC a CPU/GPU will lower it's life slightly. The frequency is not as much an issue as the voltage. Most CPUs/GPUs out live their usefulness unless you use excessive voltage and fry them.
Beenthere and geek are both right. To high a voltage can kill your CPU fast. Even if you keep the heat down with exotic cooling the voltage will fry the CPU from the inside. Heat will do the same thing, but its usually a slower process.
As beenthere also said/implied as long as you OC safely your CPU will be obsolete long before the effects of OCing catch up to it. My usual advice is to do a LOT of reading. OCing isn't just something you decide to do one day and get it done. You need to know a lot before you start messing around with your BIOS.
If your not carefull when you overclock you will shorten the life of the cpu, you want to make sure that the overclock is not too eccessive and all the settings are made so that the cpu runs stable with little heat issues. It is not a good thing to overclock to a high level and think that just because you have this behemouth cooling heatsink that you are ok. A good overclock is one where you can be satisfied with up to 1ghz over stock. Just for example I have a 980x that has a stock speed of 3.33ghz and I am using water cooling so I could clock it up close to 5ghz but instead I am running it at 4.2ghz and have been running it that way for a year and no problems. If you were to overclock and the temps were 70 to 80 c all the time then you would definatly shorten the life span.
thats for your chip inzone. amd's would cook in days at that temp. please dont give numbers unless you know you have the same chipset, especially to noobs, as numbers vary greatly by the processor. As long as you stay within the max limits of temp and voltage listed for your specific cpu, you wont kill it. How close you get to the max temp/voltage will decide the amount of cpu life expectancy. OC'ing is a great tool, but do your research first, and find someone who is educated to help you. Second, find somebody with your exact cpu! this is important as every cpu is different, especially intel to amd. And remember, not every chip is the same. some are great OC'ers, others suck!
Follow some simple rules, have some fun, and you should have no problems. Like stated earlier, stay within these rules, and technology should catch up long before your cpu dies.