I can do no better this morning than to link to my revered Captain's Blog, Fortune managing editor Andy Serwer's discussion of the most valued companies in the current marketplace. The list is topped by Exxon ( XOM), which is followed closely by Microsoft ( MSFT) and Wal-Mart ( WMT). Close on the heels of the big three are Apple ( AAPL), whose market cap towers majestically over its actual revenue, and Berkshire-Hathaway ( BRK.A), whose perceived value is driven by the general feeling that Warren Buffett, the Oracle of Omaha, can do no wrong, or more accurately that even when he does do something wrong, it's more right than other people's right, if you take my meaning. If Warren doesn't know what's going on, nobody does. What strikes Andy in this list how sensible it is. Here's what he says: To me what's most instructive here is what these market valuations say about our economy and us. Each company has its own place, right? The most valuable company is our biggest energy source, Exxon. Microsoft makes the brains of what makes most of our PCs run. Wal-Mart is our biggest store. Berkshire, you could argue, is the best of American business, overseen by a genius. And Apple, run by another business genius, is kind of the cool future company. Its products are all about unlocking the promise of technology to make our lives more productive and more fun. Right now, Mr. Market seems to think that's a pretty powerful formula. That's a persuasive argument. Each in its place and a place for each. Energy. Technology. Even at the bottom of the top ten, a representative of the poor, battered Finance sector, in JPMorgan Chase ( JPM). And yet... Buried in the list there's another take, isn't there? Looking over it again, you have to wonder how much of the value of these enterprises is driven by a factor that is highly irrational: their stock price. How much of Apple, arguably one of the great companies in history, is driven by the perception that their leader is a genius, one of a kind, totally non-fungible? Can't the same be said for Berkshire Hathaway? In fact, how much of any company's stock price is at the whim of the idiots, hedgers, madmen and demented wizards who are out there every day, gambling on the future and forgetting about the past?