Does OC really downgrade a products life-time?

Depends how smart you are about it. If you stay within the manufacturer's temperature and voltage limits, short of a random failure, the system will be obsolete long before it fails from any overclocking side effects.

I have been overclocking for years and I have never had a CPU failure from overclocking. For that matter, I have never had a CPU fail.
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Overclocking since 1978 - Z80 (TRS-80) from 1.77 MHz to 2.01 MHz

Same as jsc - a mild O/C won't hurt anything. The first sign of trouble is when temps start getting too high. Keep temps sensible and all is good.

Hmmmm, then when I get my new CPU I guess I'll be posting on how far to OC it!

You can go to the limit of the manufacturer and little beyond. he limit they give is for safe usage of there cpu. If you have good cooling and the cpu never get too hot 70-75 C. max at full load for 4 or 5 hours, it will be ok.
I have an i7-920 for 2 years now It's oc to 4,2 ghz. I never have a BSOD or anything like that. cooling cooling cooling
Have a nice day

sensible oc is not that harmful but always check the temp. if the temp becomes alamlingly high then avoid oc , better go to the default settings and then try oc kepping temp within specified limit.

I have overclocked 3 of my last 4 Core2 processors to the outer edge of stability as defined by 24 hour Prime95 test runs. My systems are in good cooling cases (Antec 900's) with good heat sinks (one TRUE and two Zig Dark Knights. All systems have reached core speed limits before reaching voltage or thermal limits. And I leave EIST enabled.

GA-EP45-UD3P | Q9550 OC'd to 3.6 GHz (425 MHz X 8.5) C3 stepping  
GA-EP45-UD3L | Q6600 OC'd to 3.6 GHz (400 MHz X 9)
GA-EP35-DS3P | E7500 OC'd to 4.1 GHz (373 MHz X 11)
GA-G41M-ES2L | E6500 OC'd to 3.87 GHz (352 MHz X 11) Motherboard limited

i have overclocked every cpu and video card i have ever owned since the original Pentium 100mhz (ocd to 133) and Nvidia's original 3D card - Riva 128. NONE of them ever failed. Only when you start really pushing things to their limits and don't use proper cooling will you get problems. Keep temps well below the components maximum.