This worked for me (on Ubuntu 11.04):
rmmod hid_magicmouse; modprobe hid_magicmouse scroll-speed=45 scroll-acceleration=1
Once you've adjusted the scroll speed and acceleration to your liking:
echo "options hid_magicmouse scroll-speed=45 scroll-acceleration=1" \
This improves the scroll speed and acceleration, but it does not scroll quite like it does on Mac. Specifically, it does not have the smooth inertia/momentum effect that causes the scrolling to "coast" to a stop when you flick your finger across the surface. Instead it jerks to a stop immediately when you lift your finger off the mouse.