CNBC, day trading, the Motley Fool, Silicon Investor -- not since the 1920s has there been such an intense fascination with the U.S. stock market. For an increasing number of Americans, logging on to Yahoo! Finance is a habit more precious than that morning cup of joe (as thousands of SBUX and YHOO shareholders know too well). In Irrational Exuberance, economics professor Robert J. Shiller examines this public fascination with stocks and sees a combination of factors that have driven stocks higher, including the rise of the Internet, 401(k) plans, increased coverage by the popular media of financial news, overly optimistic cheerleading by analysts and other pundits, the decline of inflation, and the rise of the mutual fund industry. By history's yardstick, Shiller believes this market is grossly overvalued, and the factors that have conspired to create and amplify this event -- the baby-boom effect, the public infatuation with the Internet, and media interest -- will most certainly abate. He fears that too many individuals and institutions have come to view stocks as their only investment vehicle, and that investors should consider looking beyond stocks as a way to diversify and hedge against the inevitable downturn.