ubuntu 13.04 on low end machines

I'll add two more tips to that. Switch Unity to llvmpipe rendering (low graphics mode) which does more than all other tips combined. Lower the OpenGL rendering quality.
Here's a complete Unity speed-tweak-list for reference:

• install compizconfig-settings-manager and run it
• in the OpenGL-plugin set the rendering quality to fast
• disable the Animations and Fading Windows Plugins completely
• In the Window Decoration plugin set all shadow values to 0 (or minimal value)
• enable llvmpipe rendering by running this command

.

echo "export UNITY_LOW_GFX_MODE=1" | sudo tee /etc/X11/Xsession.d/99force-llvm

• reboot.

http://www.reddit.com/r/Ubuntu/comments/1ci7op/speed_up_unity_on_old_hardware/c9hmam8