mebhow would strobing the monitor's backlight introduce input lag? Did you guys actually measure the difference or are those just anecdotal statements?
http://www.blurbusters.com/zero-motion-blur/lightboost-faq/LightBoost does increase input lag by half a frame.
Since input lag for top edge of screen can vary from bottom edge, and strobe backlights give interesting behaviors — For the average ASUS/BENQ 120Hz LightBoost screen, non-LightBoost TOP/CENTER/BOTTOM is 3ms/7ms/11ms while LightBoost TOP/CENTER/BOTTOM is 11ms/11ms/11ms. This averages out to half a frame added input lag (3ms -> 7ms) with LightBoost.
HOWEVER… The elimination of motion blur actually can improve human reaction times in situations where you are tracking eyes on moving objects all over the screen. The lack of motion blur reduces human reaction time significantly enough to more than outweigh the extra input latency, especially for FPS gaming and many others. Check out the improved BattleField 3 scores with LightBoost as an example as how increased input lag doesn’t necessarily mean worse scores. Unless you play in a very bright room at daytime, the loss of brightness will hurt your game more.
Players that stare stationary only at crosshairs at all times even during strafing/turning (no eye movements away from crosshairs), will not benefit much (if any) from LightBoost. But if you track your eyes (e.g. http://www.testufo.com/eyetracking when turning ON/OFF LightBoost), eye tracking creates display motion blur that makes it harder to track moving objects, slowing down your reaction time for these situations.
The question is very person specific: Deciding if LightBoost benefits outweigh the very tiny input lag it adds (half a frame – 4ms). It definitely does for many people, but not necessarily for everyone and every game. For example, it will benefit fast FPS far more than, say, World of Warcraft.
personally I actually tried turning it off for a couple days after that last discussion thread and found it significantly more difficult to hit shots - aiming is more about understanding their animations and where they want to move next as opposed to just reaction time
since the model is just a blur while they're jumping or strafing @ 144hz - having an extra half a frame of input lag vs. being able to clearly see their model is not worth the tradeoff (to me)