(FORTUNE Magazine) – If you were to put together an A to Z of power in America, you could argue about whether it starts with Ashcroft or Aaahnold, but there is every reason to think that it should end with Tim and Nina Zagat. No one has killed himself over a Zagat rating, as French chef Bernard Loiseau is said to have done when he feared he was about to lose a Michelin star. But the Zagat guide hasn't been around as long as the Guide Michelin.

The 2004 edition (the 25th) of the Zagat guides arrives in stores this year heralded by controversy. In New York City, a little Brooklyn restaurant with a pleasant garden called the Grocery scored a stunning 28 on Zagat's zero-to-30 scale, ranking it with Bouley, Jean Georges, and several other places named after star chefs and setting off a point and counterpoint in the city's press. In Los Angeles, David Shaw, a columnist for the L.A. Times, was so dismayed by one restaurant's inflated Zagat rating that he called--this is his word--for the execution of the chef.

I have always been intrigued by the mysteries of the Zagat guide. Why, for instance, did Planet Hollywood (now defunct) regularly score lower than the Hard Rock Cafe? At the other end of the spectrum, why does Paris have just six restaurants rated 27 or higher for their food, while Dallas has 14? Reasoning that all this could be resolved without bloodshed over some nicely seared black bass, I did the obvious: I invited Tim and Nina to lunch.

Should you have a chance to dine with the Zagats at one of New York City's fancier restaurants, take it. Not only will the chef send your table free raw fish, but after 19 seconds--I timed it--Tim will ask for more. Tim Zagat once asked Sirio Maccioni, the great New York restaurateur, how he recognized the New York Times restaurant critic beneath her wig and dark glasses. "Don't you think," Maccioni said, "that if a tank rolled into my restaurant with a hat and wig and dark glasses, I would still know it was a tank?" Now Zagat himself is the tank, and since the Zagats don't vote in their own surveys ("Caesar's wife ...," Nina says), they don't even need disguises. "It's nice to see what a restaurant can do when they really try," Tim says.

"What is your best fish?" he demands, after we take our table at Esca ("a restaurant to return to again and again"--Zagat 2004). The menu sits unopened by his elbow. "Do you have a branzino? What does the chef say? Is the chef around?"

The chef, David Pasternak, is already on his way. That is good, because Tim is on a diet and needs attention. Tim is often on a diet. This one allows "fish, meat, greens--no carbohydrates." Tim's diet two weeks earlier, Pasternak tells me later, called for only pasta. The first time Pasternak met him, years ago, Pasternak says Tim needed a special diet for a case of gout. (Tim denies the gout but admits the diets.)

If the key figures of democracy can be divided into rabble rousers like Tom Paine and mandarins like Thomas Jefferson, the Zagats fall into the second camp. Both Nina and Tim are lawyers--Tim (Eugene H. Zagat on his driver's license) a former corporate litigator, Nina a family lawyer for the very rich. They met when they were both working in the Paris offices of white-shoe firms. They put together their first guide in 1980 as a lark, asking about 100 acquaintances to rate New York City restaurants. At a time when high and low mixed less readily than today, it reviewed both four-star places like Lutece and finds in Chinatown.

That first survey, on two mimeographed pages, included ratings that one just doesn't see in the current guides: the old battleship Luchow's and the supposedly romantic Sign of the Dove came in at a dismal 7 for food. Those restaurants were awful. How awful? In 1973 a New York businessman chose to be arrested rather than pay for the charred and "pea-sized" Chateaubriand he was served at Sign of the Dove. The charges were dismissed when nobody from the restaurant showed up to defend the food. Zagat's is part of the reason that few places that bad are still in business.

Two decades after the Zagats started selling their survey in the city's bookstores, the annual Zagat guide to New York City restaurants sells 650,000 copies. To hear the Zagats tell it, professional critics are obsolete. Nina's faint praise: The newspaper critic's review "is fun to read--when you have some time on a Saturday and want to enjoy the literary experience. Our books are completely different. They're about how to help you make a decision."

Yet, as readers have noticed, it has become harder and harder to use the Zagat guide to make a decision. Take that 28 rating for the Grocery in Brooklyn. "It has an 18 for decor--it's not Le Bernardin," Tim tries to explain. "Everybody knows how to read the numbers to say that it is what it is." As Tim confronts the biggest grilled snapper I have ever seen, I contemplate his curious tautology. If it is what it is, what exactly is it?

Meanwhile, all around the Zagat world, the ratings creep upward. In the first survey the average for all restaurants was 16.5, at the low end of the guides' "good to very good" range (16-20). Now the average New York City food rating is 19.93. Restaurateurs themselves are often skeptical of the ratings. "There are people who vote for the French Laundry who've never even been there," say Nancy Oakes, the chef and owner of Boulevard, Zagat's "most popular" San Francisco restaurant. Cheating is not unheard of. "It almost begs for ballot stuffing," says John Long, former editor of the Cleveland Zagat guide. "Sometimes I could tell from the handwriting on the surveys."

What to do? Option one: Eat at Jean Georges, as the Zagats do. ("It's like Tim's cafeteria," Zagat's publicist says of the $90-a-meal French restaurant.) Option two: Get involved. The next time you gag on a plate of shark and abalone tartare with elderberry reduction, at least you can go online and slam the restaurant. The Zagat guides won't save you from every bad meal, but you'll no longer have to risk arrest to get revenge for a dish served cold.

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