I'm planning on building my first rig with an i5-3570k, and I plan on mostly gaming. I've heard that the primary reasons not to overclock are the risk to burning out your CPU (which from the looks of it looks easy not to do since there's many ways to keep it cool), and the other reason is that it shortens the lifespan of the component.
My concern is with the second reason because I like a future-proof rig, and that means going as long as possible without having to buy new components all the time. Would overclocking drastically decrease the time before I need to buy a new CPU? Or could your CPU last (relatively) as long, overclocking or not?
If the overclock is done correctly (staying within acceptable voltages etc.) and temperatures monitored, the life of your components should not decrease appreciably. Your game performance can increase quite appreciably and yes, there are a multitude of ways to keep your components cool. There is still a risk of damaging components though. With that in mind, you may want to hold off on overclocking for when you desire a little free 'upgrade'. That will also give you time to research what you want to get out of your overclock.
Hope it helps some
CPU life can't really be measured as each chip will be different. The way a chip "dies" over time is the silicon based materials ends up shrinking from heat and voltage running through it for so long. So one thing that does determine lifespan is definitely going to be how long it's ran for. A processor that is used 24/7 will wear out before a processor that is only ran for a few hours a day.
The biggest determination of life is the voltages. Higher voltages turn into higher temperatures no matter what cooling device you have. Even though you're supercooling a processor doesn't mean that voltage isn't making the heat on the die before it's transferred to the cooler. So higher voltages can diminish the life of a CPU depending on how much is thrown into it.
Heat is the main killer of processor dies as it does the major contributing to the shrinking. However with lower voltages usually heat can be controlled with a good heatsink. I try to stay at lower temperatures simply to be safe with the overall life of my CPU as I don't really know when I'll want to replace my current chip.
Overclocking and running the chip at a higher frequency can also contribute but mainly because of the higher heat output of the processor during loads. Remember, overclocking increases the cycles the chips do. A processor running at 3.4Ghz is going through 3.4billion cycles a second. So adding 600,000,000 cycles per second is a pretty big increase. However the heat with just adding cycles doesn't always increase greatly at all.
I suggest following what C12 said by going with stock until you want that "free" little boost. You'll probably end up being like most of the people who I build systems for who ask me to overclock their gear before they get it. I simply tell them try it out first and then decide and for the most part everyone enjoys their rigs at stock speeds for years.
There has already been one good, detailed answer given. I'll take a different approach and offer you a different angle to view the decision from.
Personally, I don't like the phrase "overclocking"- it paints a picture of pushing something past it's limits and, with your concerns being a good example, tends to imply risk as a part of it's very nature. I would say a more accurate and constructive description would be simply "tuning" or "clock adjusting". The system BIOS is going to instruct the processor, memory, or chipset what speed to run at regardless of whether you leave it set to automatically do so, or whether you specify the exact settings yourself. All components are mass produced, and the default speeds are set low enough to ensure that every unit can produce that level of performance, even with the variance in unit quality that's inevitable with the production process. So, realistically, the factory clock speed is going to be far short of the safe potential for about 90% of the individual units sold. This also means that in most cases, the default voltages running the default clocks are actually higher than your particular processor actually would require. So, if you remove the idea of default clocks being the baseline, you technically are already increasing the rate of wear and tear on the processor compared to how it could be manually tuned for the same performance.
In reality, you are going to almost always upgrade before burning out any component as long as you keep within a reasonable voltage range. So, if you want to be safe, the most sensible choice isn't to not adjust the factory clocks, bur rather to find what is considered the top of the "risk-free" voltage range for your processor, then work on finding the fastest stable clock speed that would be possible using that voltage limit.
There are definitely those of us who "over"clock and know we are running our systems into the ground while doing so, but rational, sensible adjustments to a system are nothing to fret about making. It's only those who haphazardly start tinkering that end up generating the stories and perception that there is some degree of risk that is unavoidable.
+1 to what ocmusicjunkie said. He nailed it right on the head. I completely forgot to mention that as well. Most of the Ivy/Sandy bridge CPU's at all stock settings run higher voltages than the processor ever needs. My 2600k is a perfect example.
Default settings range from 0.8v at an idle to all the way past 1.35v at full load simply at the stock 3.4Ghz with automatic voltages.
My "manually tuned" settings with the voltage offset being at -0.020v and the clock at 4.4Ghz ranges from a sickening 0.9v at idle to a maximum of 1.312v at full load. So I cleared a 1Ghz overclock and actually dropped the voltage it was sucking down at stock.
Ah ok, I see what you guys mean now. So it's actually better to take the time and adjust the CPU so that it stays at a recommended temperature and takes advantage of the volts already given to it? I'll keep that in mind then. However since this is my first build, I'll probably take the advice of holding off on messing with the clock speed, so as not to void my warranty, just in case I mess up on my first build and need to send the component back.