Linear and fast mouse speed in OS X Lion. Possible?
A recently released app called SmoothMouse will do exactly what you want, and (in my opinion) works much better than the other alternative mouse drivers.  It's free and available here: http://smoothmouse.com

On top of offering options for both linear and Windows-like acceleration curves, it also removes the 32ms of lag that OSX typically imposes on mouse cursors.  To me, this is just as essential as changing the acceleration.

This thing is really pretty close to the holy grail - great-feeling mouse movement on OSX.