Just to revive this thread, seems like there's a lot of misunderstanding here.

I'm going to define vdroop loosely in layman's terms and just say that the voltage to the processor DROPS when the CPU is under load instead of maintaining a constant voltage.

Indeed there are some articles which state 'vdroop' as a feature to prevent damage when switching from low to high loads. I am unable to verify this.

However I believe the problem that Asus motherboards face are of a different nature.

The vdroop I experienced in my Asus P5KR, a P35 motherboard causes masses system instability under relatively low overclocks.

Rig:
Q6600 G0 stepping 2.4 ghz default
2 gig Team Xtreem DDR2 1066 RAM
Asus P5KR with latest BIOS
850W Gigabyte Odin
2 x 4850 in Crossfire mode
Vista Home Premium

MY BIOS DOES NOT HAVE THE VOLTAGE DAMPENER OPTION!!!!! Apparently it also doesn't work for the P5K vanilla mods even when listed, only working on the Premium P5Ks.

Tools used:
CPU-Z
Speedfan
Lavalys Everest
Prime95

First of all this is what the situation was before I did any mods

a) When set in BIOS under Auto, voltage is reported in CPU-Z as around 1.385 which fluctuate in around a 0.07 range.
b) When set in BIOS under 1.400, voltage is reported at around 1.375 in CPU-Z which then fluctuates again in around 0.07 range
c) These fluctuations happen when the system is under load for example when PRIMING and the voltage REMAINS below the set voltage.
d) Errors occurred in the Prime95 frequently and system blue screened under both Auto and 1.35 V settings. 1.4 V still crashed but less.
e) Could not OC past 2.8 ghz

I also tried this with my old Intel Core 2 Duo 6400 and could not go past 3.2 ghz.

Now after I applied a pencil mod to my P5KR
a) when bios set to 1.375, it is reported as 1.375. very little fluctuations around the 0.01 range.
b) Under load, voltage was maintained at 1.375 with it peaking up to 1.384 during the transition from low load to high and then stabilized again at 1.375. Nothing to be alarmed about.
c) No errors during Priming at 3.0 ghz with 333 mhz FSB and 9 multiplier. RAM was set at 1:1 at 667 5-5-5-12 just for troubleshooting purposes.

Therefore...if you are overclocking and finding that your system is unstable even at moderate overclocks, time to take out that 2B pencil and start shading Just google it up P5K pencil mod and find a pic that shows your setup. Do note that the P5K Premium has a diff layout than the regular P5K (and P5KR).