If you feel like your MagicMouse tracks a little weird, you may want to try the following setting:

(in your terminal write the following)

defaults write .GlobalPreferences com.apple.mouse.scaling -31000

Make sure you logout and login again after doing the following change.

NOTE: Make sure you don't change the tracking speed after doing this, this will reset the change you just did.

Kudos to marco for this tip.