Ubuntu 10.04 Flash Videos have tearing/lines Solution
This is what I call a ridiculous bug in compiz that causes it.
The solution/To fix it just install "compizconfig-settings-manager"
Open it up and Navigate to General Options -> Display Settings
Set the "Refresh Rate" to the current refresh rate of your monitor.
For ATI cards with slow window dragging/response supposedly disabling "Sync to VBlank" fixes that but otherwise leave it as is.
You may need to restart X to make the settings apply (I can't remember) but I'm glad to have solved this annoying Compiz bug.