Edit: After further research, I found that this fix only adjusts the speed at which your mouse moves. It doesn't do anything for the acceleration curve.
I recently picked up a Magic Mouse and discovered that I like almost all of its features. The biggest headache is the funky mouse acceleration curve that it applies by default. When you make small movements, they barely even register on the screen. When you make big movements and slow down a little mid-move, the pointer slows down much too rapidly.
A quick Google search revealed a support discussion post where users were discussing possible solutions. Someone suggested running this in the terminal:
defaults write -g com.apple.mouse.scaling -1
That improved things a little for me, but it's not perfect. If you adjust the tracking speed in System Preferences after running this command, the acceleration curve will be reset to the default.
Update: After some tinkering (and further Googling), I found that 0 or .1 seemed to work better for me than -1.
hi... i really like this post but it doesn't seem to do anything for me on the latest update of osx 10.6.6. I'm wondering what your current solution is?
There IS a solution, and it is called Magic Driver. It implements all kinds of additional features with the mouse (swipe, drag, multiple clicks etc) but for me most importantly it allows you to change the sensitivitiy of the tracking AS WELL AS the tracking speed. In other words, it supports adjusting the acceleration curve! I don't know where I'd be without this driver - my Mac just wouldn't be usable. I love it.
http://plentycom.jp/en/magicdriver/index.html
However, the BAD news is that the developers are thinking of stopping development, and since the current beta expires in April, that effectively would mean no more Magic Mouse. They told me they are seriously considering dropping any more development very soon. So download the driver and if you like it and it solves your problems, write to the developers (email is on their website) and tell them NOT to stop development on this! I for one would gladly pay them for this product if they continued development and bring out a release version. By the way, I have found the driver to be fully functional in its current beta state.