In Ubuntu Gutsy Gibbon a user of the software mactap have found an error in applesmc which now cannot use movement sensor:

cat /sys/devices/platform/applesmc.768/position
cat: /sys/devices/platform/applesmc.768/position: Error de entrada/salida

You can find (in spanish) the thread here:

Also i would like to tell you that mactap 0.0015 have been released:

http://magarto.com/blog/archivo/2008/01/04/mactap-ejecutar-acciones-mediante-toques-en-la-pantalla-en-el-macbook-en-gnulinux/#comment-3911