Essentially, the article describes (and prognosticates on) a relatively novel kind of exchange. Rather than selling securities in companies (aka stock) or derivative instruments, information exchanges sell futures on events yet to happen. That probably doesn't mean much to you unless you follow the markets, so here's a longer explanation cribbed from the article:
Take the presidential election: people could bet on George Bush by buying a contract that paid a dollar if he won and nothing if he lost. Anyone certain of a Bush victory should have been willing to pay up to a dollar for the contract. Anyone confident that Mr Bush would lose could have sold such a contract, expecting to pay nothing when the result came. With many participants buying and selling in this way, the market discovered a price for the contract—in effect, its best guess of the probability of a Bush win.
Think about that for a second. This is a mechanism that exploits people's (enlightened?) self-interest, in the form of their desire for money, to collect their opinion on a particular topic. It discourages the intentional and unintentional fraud inherent in phone surveys, because of the monetary stake. It also introduces a novel (for the opinion-gathering industry) and well-tested set of tools for opinion analysis: the discipline of financial economics.
That reminds me of the proof of Fermat's last theorem. (Simon Singh's account is a fantastic one, in case you care.) The proof relied partially on the realization that two very disparate branches of math were, in fact, solving the same problems from very different angles. Things difficult in one context are easy in the other, and vice versa. So perhaps thinking of opinion-modelling as a financial market will increase the accuracy of the opinion marketing. Additionally -- and this is a topic for a different essay -- could the same be true in reverse?
Another interesting aspect of information markets that isn't adressed in the Economist article is that these markets, if they become popular, allow people to monetize their knowlege in a relatively direct way. If I know more than the world in general does about a topic that's traded on an information exchange, I can exploit that knowledge for personal gain. Entrepreneurial current-events analyst could very well be a respected career choice.
Capitalism wins again!