Well it didn't really originate with Anandtech.com, far as I know, but with Tom's Hardware when they reviewed Viewsonic's 8 ms monitor:
http://graphics.tomshardware.com/display/20050526/viewsonic-08.html
It really comes down to overdrive implementation. Overdrive is a way to improve the response time of LCDs, by having the driving voltage be past that of what's desired for one frame (or more), before settling down on the desired frame. This is because small (i.e. gray-to-gray) transitions for LCDs are traditionally slow, but large (i.e. black-to-white) transitions are much faster. So if you are going from 0 to 175, say, you tell the monitor to make the first frame be 200, for example, with the rest be 175. This way, the monitor tries to go to 200, but over one frame it "only" reaches 175; it then spends the rest of the time at 175, the one that's desired in the first place. This is completely a programming trick (i.e. via controller circuitry) and does not change the characteristics of the LCD panel itself (brightness, contrast, etc.) in any way. The LCD panel itself is just as slow as it's always been, just that it's now masked because of overdrive.
Viewsonic's implementation is somewhat different. Because they want to market a better number, they have the pixels go over what's desired, then count _only_ the rise part -- and omit the part afterwards where the brightness goes way above what's desired then settle down. This thus generates a sparkle effect -- previously dark parts of the screen suddenly flash, because of the pixels going above the desired value. This effect is increased in dithered images, like movies, because each pixel is actually rapidly changing its brightness (with the eye averaging out the effect), but the circuitry doesn't recognize that the pixels' brightness are meant to be averaged, and so thus overshoots them and making sparkles. And I would really recommend using a DVI connection rather than normal VGA; if the clock/phase settings are not perfectly set, each individual pixel actually changes its brightness quite a bit, thus generating a watery effect if they are far off from ideal. You can imagine what that's like with a sparkly monitor.
(For more about close/phase settings and a handy screen to mess around with and see what it's like when your clock/phase are not set correctly, see www.techmind.org/lcd/phasexplan.html )
So when Viewsonic came out with their 4 ms monitor, what really happens is that, yes, it does take only 4 ms to go from 0 to the desired value -- but then it spends the rest of the 12 ms of a normal 16 ms frame (assuming you're running at 60 Hz like most people) going past that desired value. Considering Tom's Hardware already reported the effect with Viewsonic's 8 ms monitor (which spends "only" 8 ms going over the intended value), you can imagine what the effect will be with a 4 ms monitor. When Tom's Hardware tested a 0 to 175 brightness transition, for example, it first shoots up to 210 brightness (but the 0 to 175 part of that transition does take only 4.5 ms), then settles down to within 10% of 175 some 26 ms later, for a total of 31 ms from when the value was requested. Viewsonic considers 210 brightness to be close enough to 175 that it can be omitted from the response time measurement; I leave it to you to decide for yourself if being 20% off from the desired color is close enough.
In fairness though I haven't seen the monitor, so I have no idea if the sparkle effect is actually that noticeable with either monitor. That's sort of a YMMV thing I guess, so you might want to look at it in a store before deciding to not buy it. But I really don't like how they're perverting these specs in order to market a better monitor and thus confuse the consumers, which is why I posted that rant.
I should mention, this has nothing to do with overdrive itself, but only to do with Viewsonic's implementation of it. Overdrive itself is a perfectly valid way to speed things up and does not generate any sparkles, unless you overshoot so far that it becomes noticeable, i.e. Viewsonic's method. The original implementation was to set the overshoot value to be just enough so that the pixel reaches the desired brightness by the end of the frame.
The part of Tom's Hardware when they talk about how Viewsonic implements overdrive (for the 4 ms monitor) is here:
http://graphics.tomshardware.com/display/20050602/viewsonic-05.html
Read onwards from that page, they have actual measurements of the effect to back up what they say.
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