In a typical day, I might write two tweets, peruse 15 blogs (Jason Kottke and Penelope Trunk are two must-reads), and watch James Brown dance on YouTube. If it’s a really fun day, I’ll read more blogs, scour the Web for movie reviews, browse eBay, Google myself, and spend more time on Twitter. None of this costs me a penny, and yet I am producing plenty — namely, my own interest and amusement.

More and more, “production” — that word my fellow economists have worked over for generations — has become interior to the human mind rather than set on a factory floor. A tweet may not look like much, but its value lies in the mental dimension. You use Twitter, Facebook, MySpace, and other Web services to construct a complex meld of stories, images, and feelings in your mind. No single bit seems weighty on its own, but the resulting blend is rich in joy, emotion, and suspense. This is a new form of drama, and it plays out inside us — with technological assistance — rather than on a public stage.

Online, you can literally create your own economy. By that, I mean you can build an ordered set of opportunities for prosperity and pleasure, analogous to a traditional economy but held in your head. There is no obvious monetary transaction, but you’re using your limited resources to get a better deal — the very essence of economics. In fact, “economics” comes from oikonomia, the ancient Greek word for household management, and the modern practice of economics is returning to that idea.

The traditional gauge of economic success is profit, but over time we’ll find that such statistics as measures of GDP tell us less and less about broader efforts to improve human well-being. Much of the Web’s value is experienced at the personal level and does not show up in productivity numbers. Buying $2 worth of bananas boosts GDP; having $20 worth of fun on the Web does not. And this effect is a big one. Each day more enjoyment, more social connection, and, indeed, more contemplation are produced on the Web than had been imagined even 10 years ago. But how do we measure those things?

That question — and I don’t yet have a full answer — reflects the state of flux we’re in today. We’re going through a lot of adjustments, and not just in real estate and finance. Free stuff on the Web has made this economic downturn more severe. For many of us, the Web really is more fun than a trip to the store, which makes it easier for us to cut our spending. Although the iPhone has been earning lots for Apple, our spending on high-tech goodies does not make up for falling demand elsewhere. A PC and broadband cost something, but for those millions who have paid up, further exploration is essentially free.

Nor do most Web activities generate jobs and revenue at the rate we saw with past technological marvels. When Ford was growing early in the 20th century, it created millions of jobs and helped to build Detroit into a top-tier city. Today, Facebook creates lots of voyeuristic pleasure, but much of the “work” is done by software and servers, and the firm hasn’t transformed Palo Alto. Web 2.0 is not filling government coffers or supporting many families — and may be hurting some. (Just ask a newspaper reporter.) Everyone on the Web has heard of Twitter, but as of this spring, fewer than 50 people work there.

That all sounds scary, yet there is a bright side; I call it the “human capital dividend.” The reallocation of consumer time into the “free sector” on the Web will liberate the efforts of many producers and intermediaries, just as the automobile’s advent shifted workers out of making buggies for the horse. In fact, it’s an economic miracle that Twitter can get by with no more than 50 employees. It’s not quite a perpetual-motion machine, but if other parts of the economy were equally efficient, we’d all be swimming in free or near-free stuff.