Fyrd/caniuse — pull request #133 by wheressyb (2013-02-12 15:17:23+00:00)
Title: Update features-json/viewport-units.json

The spec states the following: "The viewport-percentage lengths are relative to the size of the initial containing block. When the height or width of the viewport is changed, they are scaled accordingly."

Since Chrome doesn't support the latter part this, I consider the feature not usable in its context.