If the OP is talking about "REAL" apps like world web browsing, office, email, etc.. then you will see NO difference. Thats not the point of overclocking. Overclocking is about getting more out of the CPU for the applications that require it - Encoding, gaming, folding etc.. Thats where turning a sub $200 cpu/gpu into a top of the line cpu/gpu pays off.
You can get a office machine for $300 if thats all you do.
The other benefit to the consumer is the ability to allocate funds to the part of the system that needs it the most for the apps you're using. For a gamer, getting a $200 cpu and overclocking it, allows you to put that money to a faster GPU, or other components of the build(mobo, ram, gpu, a decent monitor).
If your not all about the latest in greatest, right now if the sweet spot for the intel core 2 duo price/perfomance overclocking. But it comes at the perial of intel switching platforms.
asus p5q pro + 4gb ram combos ~ $140
~$170 for 4ghz overclock dual core (E8400) or 3+ ghz q6600
~$250 for 3.5ghz overclock q9300
$300 to $400 for the meat of the overclocking realm cpu+mobo+ram is ridiculous..
aftermarket HSF for what.. $30
I'm just waiting for deneb numbers now, but with prices like this, AMDs price/perfomance stronghold is under heavy fire.. only benefit may be am2+ denebs for another year on the platform.