Originally Posted by Dragoran
Well because the overlay can't be redirected and therefore bypasses the CM completely, which would just end up creating visual artifacts.
VSYNC should be possible using any opengl based CM like compiz or mutter "isn't currently possible at all" is just wrong ... it works just fine, if it doesn't it is likely a configuration issue.
Hmm. Even with proper configuration with compiz I still get the odd tear now and then. Admittedly it has got a lot better with recent driver/compiz releases.
You would get some visual glitches when moving/scaling windows but for a static window just sitting there it would work ok. It would also allow vsync on more than one monitor at a time.