I wouldn't even imagine overclocking a processor or exceeding the specs in any safety related system.
But as spannersatcx says, I overclock my home PC which does my surfing and gaming and SETI@HOMEing and what not. (And I do run a Celeron 366 at 458MHz every day.) Most PCs live well within the chip specs - when was the last time your home computer's CPU ever saw the 0 degree or 70 degrees C ambient temp. the CPU is usually rated for (ok, approximately that - I haven't seen the specs lately, but that's usually the commercial temp. range, as opposed to the military temp. range avionics generally uses of about minus 40 to plus 125 deg C)? Most people are happy if the overclocking worked at ambient temperatures of between say 15 and 35 deg C because their house never exceeds that tempurature. If the MTBF is lower by a few hours, so what - I can throw away a $60 chip in 4 years instead of 6 - by that time, it is almost obsolete anyway.
[See
www.overclockers.com or any of the USENET overclocking newsgroups for interesting information on overclocking.]