How do I tweak the precise mathematical curve used for the mouse acceleration in Ubuntu?
That depends on what mouse profile you're using.
This blog describes a new mouse acceleration method added to Debian Squeeze (should also be in Maverick since Squeeze used xorg-server 1.7.7 and Maverick used 1.9.0). You can read the developer documentation here.
If you look at the source, you can derive the curve based on which Profile you're using. In the patch for AccelerationProfile, you can see the function
So to tweak it, you modify whatever inputs your selected profile takes. Presumably these are set in xorg.conf (which, fyi, doesn't exist by default).
To really customize it, you can write your own function and compile your own xorg-server : D
Okay, I think I found the answer...
Something like this should do the trick: