I used to run a E8400 @ 4 Ghz without issue for a year. Upgraded to a Q9550 then upped it to 3.4 Ghz and I've been on that for 10 months. The key is to stay within reasonable temperatures and voltages. The higher these two things are, the shorter the lifespan of your components are. How much shorter is debatable, most people upgrade way before then.
yeah I OCed my cpu up to 3.9 by increasing the voltage too high and ended up damaging it so #3 it is for me. 3.8 was fine with the volatge, but I had to go and up them both - stupid curiosity and the need to overclock
I think overclockings worth the risk to get better performance. i'll probably upgrade my computer in another year or two so for me if i break something it will just be an "early upgrade" lol.
I overclock. On my old mobo, the ASUS P5N-T Deluxe, I had my E8400 @ 3.00GHz run at 4.00GHz.
Right now I'm running on a Gigabyte motherboard, and have that same cpu running @ 3.6Ghz. I'm slowely working on hitting 4.0GHz or higher, but gonna take it slow