The MacPro desktops are poorly supported by applesmc, which provides fan control, ambient light and temperature sensors. You can help this situation by:

1. Installing this package:
http://ubuntuforums.org/attachment.p...1&d=1226459872

2. Loading the applesmc module
Code:
sudo modprobe applesmc
3. Performing the tests in this post: http://ubuntuforums.org/showthread.php?t=924096

Thanks!