Shirky makes the readily defensible claim that there are billions of hours of free time, or "cognitive surplus" in the world which people can choose to use as they will. Taking the simplistic case of working 8 hours a day, five days a week, and sleeping 8 hours a day, the math is simple: there are many unaccounted for hours which people can choose to use for constructive purposes, given suitable means, motive and opportunity.
But what about during the workday, where those of us working on Enterprise 2.0 are trying to make things happen? Dare we say that there is also a cognitive surplus in the office?
Well, I dare to say so: every enterprise that is a decent place to work in has a cognitive surplus, whether it wishes to admit it or not.
Human beings are not machines that can run non-stop for eight hours a day without stopping. There are certainly jobs where there is very little downtime (e.g., phone reps in a very efficient call center, for example), but knowledge workers in particular need and do take time to reflect, to plan, to research and to evaluate. They need to time to think.
It's simply not possible or practical to predict or regiment the amount of thinking time a knowledge worker needs in order to be effective. Every one of us simply does the best we can to be efficient and effective in discharging our responsibilities.
I believe there's gold in that thinking time. It's a cognitive surplus that can be tapped into by the enterprise if the right means, motive and opportunities are presented. It is exactly what those of us who have deployed Enterprise 2.0 technology have been observing for years.
It's not a bad thing to have a cognitive surplus, and you'll never get rid of that "organizational slack." It's just a shame to miss out on the amazing things your organization could be doing with it.

