I don't know that much about mouse acceleration, but I can only tell that I really love it. At the beginning it sucked pretty hard, but once you get used to it you don't want to go back, atleast I don't want to go back. When I started playing ET it didn't matter to me if I played with a really high sens or a really low sens, I could handle both quite good. But I wanted to use them both in different situations, like high sens is really hard if the distance is big and low sens sucks if you get raped. With mouse acceleration I got the feeling that I have both low sens and a high sens, and everything in between. Of course there could be things like negative accel, but tbh I don't even know what it means and it never bothered me.