Originally Posted by MONVMENTVM
The mouse has acceleration, as do all the other mice with the ADNS-9500 and 9800 sensors like the SteelSeries Xai, Sensai, Logitech G9x, G500 and many many more and you can test the acceleration precisely enough with the method above. If you move the mouse to one direction and then move it back to the exact same spot on the pad, the cursor should also arrive at the exact same spot on the screen as before, no matter what. You can try the same with other mice that are known not to have acceleration and you will see that compared to that, the Taipan does have acceleration.
Also acceleration -- contrary to what you state -- doesn't make the mouse behave the same every time, which is because as a human you won't move the mouse at the same speed every time, which would be required for it to behave the same.
Let's assume that you would somehow be able to control that mouse in a way that you would be able to hit a reflex shot every single time. The acceleration of those ADNS-9xxx mice is non-linear. I'll give you an example of what that means:
Let's say you move the mouse at 1.0m/s and the cursor moves for let's say 1000 pixels on screen. Moving it at 2.0m/s would maybe make the cursor move for 1050 pixels now for the same physical distance as before because of the acceleration we already talked about. Due to the non-linearity of the acceleration when you move the mouse even just slightly faster at 2.2m/s for the same distance, the on screen movement would now be just 1010 counts now.
So as you can see, the non-linear acceleration makes things much more unpredictable than you would think -- and I have to repeat myself at this point: As it is just 5% you and most other people including me don't really feel that these mice have acceleration. But it does affect your aiming.
Now don't get hooked on that numbers, I chose them just as an example, although I did use the 5% max acceleration to show it's effects. 50 pixels deviation is a lot for a 1000 pixel movement, which translates to WAY more than just a small head when trying to hit somebody behind you with a reflex shot. Yes you could still do the headshot by correcting your aiming and moving the crosshair back, but this will take you more than twice as long as if the reflex shot would've been successful in the first place... so a pro that doesn't have those issues would've been able to kill you twice in that time and yet you would call him "cheater". Or just blame yourself for missing. And actually you may have killed him, had you used a proper mouse, that doesn't work against your reflexes.