Imagine if everyone in the world had two buttons on them at all times: thumbs-up and thumbs-down. Anytime anyone on the planet has a positive feeling or experience, they press the thumbs-up button. Every time they have a negative feeling or experience, the thumbs-down.
Now imagine all these billions of button presses get sent back to a central repository in real-time, over the internet, cell-networks, whatever means of communication necessary. Attached to each button press would be a timestamp and a geo-location tag.
First, you'd get an instant global zeitgeist. Interesting, but maybe by itself not very insightful. I'd guess it's probably pretty static, maybe cyclical with the time of day, day of week, or season.
But more importantly, you could surface instant anomalies. The mood in a village in Africa drops precipitously overnight, perhaps an indication that violence has broken out; a flurry of negative activity in a big European city as news of a local hero killed in an accident spreads through the public consciousness. A country experiences a collective moment of elation as a new leader is elected.
Governments, activists, and human rights groups around the world would have incredible power to find hotspots, watch for trends, and measure effectiveness of political messaging and aid campaigns on a global scale.
Twitter would like to be such a world-o-meter, but it suffers from being too obscure, too complex, and too qualitative. Arm the world with thumbs-up/thumbs-down and see what happens.