Problem with interpretting and using the IMU data
You may want to take a look of freeimu library which take care of all needed processing and present filtered and data-fused data (not just raw data) in easy to use roll, pitch and yaw format.

http://www.varesano.net/projects/hardware/FreeIMU

see demo video in which the on screen data mirror physical motion of the sensor
http://www.youtube.com/watch?feature=player_embedded&amp;v=rFvX3vZJHTQ

hope this helps