Add to /etc/environment
I don't have unity-tweak-tool installed (it's hurge) for any other reason.
The new blur code doesn't work as expected on many hardware configurations including mine. For whatever reason development chose to emulate some hardware functions in software which is much slower. The above change puts the function back in the much faster hardware.
I think launchpad bug #1222602 has some more detail.
At 78 my vision is blurry enough I don't need deliberate blur in ubuntu.