From Fortune: What Google searches say about life. An excerpt:
Tucked away inside Google Finance is the newly-launched, “Google Domestic Trends”. While it sounds like it might offer the latest in recipes for meatloaf or techniques for pressing a shirt collar, what it does is track search traffic across 23 specific sectors of the economy ranging from auto buyers, to jobs and the retail trade.
All indices use January 1, 2004 as a baseline from which a seven-day moving average is calculated. So if you look at auto buyers, you will see a more or less predictable seasonal car-buying pattern, peaking during the late spring and summer when people are looking at the new models and dealers cut prices on last year’s stock. The number of searches for cars falls off around the winter holidays before ticking up again at the end of the year, presumably for tax reasons.