I've been overclocking since my Pentium 133 mhz. So far i have never burned out a CPU. I change CPU every 2/3 years. I have a 4800 X2 reaching 2 years of use, and i had to take the OC off temporarly, because it wasn't taking the continuoes sessions of Astropulse (Seti@home).
There are 120 hours continuos sessions. Of 100% CPU usage.
I think it is my crappy mobo giving out, because it got a 500mhz OC (2.5 to 3.0) with a 1.350v. The default is 1.325v. Done with a bit of sense ( goodthermal paste and non-stock cooler) OC'ing is safe. Hell i got a Athlon 1500+ that was "transformed" into Athlon 1800+ and to this day ( more than 5 years) still works flawslessly. My little brother still plays wow on it.
Now, OCing is free performance. And doing it right, knowing a bit about it, represent no problem.