From a speech he gave at the Web 2.0 conference in April 2008: Clay Shirky tracks the history of our cognitive surplus, explaining what we could, or need to do with it:

So how big is that surplus? If you take Wikipedia as a kind of unit, all of Wikipedia, the whole project—every page, every edit, every line of code, in every language Wikipedia exists in—that represents something like the cumulation of 98 million hours of human thought. […]

And television watching? Two hundred billion hours, in the U.S. alone, every year. Put another way, now that we have a unit, that’s 2,000 Wikipedia projects a year spent watching television. Or put still another way, in the U.S., we spend 98 million hours every weekend, just watching the ads. This is a pretty big surplus. People asking, “Where do they find the time?” when they’re looking at things like Wikipedia don’t understand how tiny that entire project is, as a carve-out of the cognitive surplus that’s finally being dragged into what Tim O’Reilly calls an architecture of participation.