> Not entirely (un)related: I wonder if the earth's rotational speed could be changed significantly if the entire 6 billion (6.000.000 or 6,000,000) of us were to run simultaneously in the same east-west direction? You see, I've made a rash promise to increase the length of the day, and I'm wondering whether the most effective way is to redefine time or decrease the earths rotational speed.

Not sure, but if it did, the second everybody stopped running, the rotational speed would be back to what it was before.