Moderate increases in voltage(~10&#37 are not dangerous at all provided you keep core temperatures under control. I don't think there's been a single documented case of anyone burning out a CPU while running moderately increased core voltage. It is highly debateable what is the absolute max safe voltage so it's up to the individual to decide what they are comfortable with.

Naturally running any piece of equipment beyond spec will shorten it's life. But if the original lifespan of a CPU is 10+ years and your OC shortens it to 6, does it really matter? Not many people keep their hardware that long, especially overclockers.