http://www.venehammerschlag.com/worldjumpday/
Some how I doubt all the people in the world have enough mass to pull this off, and if they did, it would likely cause earthquakes (from the mass impact, not the orbit change).
Please do not join in if you are on the Goldengate Bridge or the edge fo a cliff.
In other news, when is World Skip Day where everyone just acts silly and skips to the theme of The Smurfs?