Re: Nvidia Ion, Ubuntu Karmic and Composite
VDPAU's tear-free blit mode can only work when the window it's rendering to is not redirected (i.e. you're not running a composite manager, or the window is full-screen and you've enabled Compiz's "unredirect fullscreen windows" option).
When a composite manager is enabled, it's up to it to perform the vblank syncing. Please make sure that Compiz's "detect refresh rate" option is disabled and that the refresh rate slider is set to twice your screen's actual refresh rate.