I use Ubuntu 12.10 with Unity and I run a mid range ATI 5000 series GPU. Performance was surprisingly good in 12.10 after a fresh install (upgrade made performance horrible) but while playing Flash/HTML5 video things slowed down considerably, and using Super + W (expose) was much slower.
I searched around for some quick tips and found two that have apparently improved things significantly.
sudo apt-get install compizconfig-settings-manager
Then go to the CCSM and the OpenGL plugin and disable “Sync to Vblank”.
Go back to CCSM and then the Composite plugin. This time disable the “Check refresh rate”.
Expose is now much quicker/ smoother. Noticeably so – even while I’m playing video in Chrome. The difference is like night and day – I can reload pages/ tabs alongside the video and move windows around and it’s all smooth.
Make sure you’re on the latest ATI drivers. Due to Valve pushing for better Linux drivers the most recent versions (12.8/12.9) feature vastly improved performance.