The idea of Farecast.com used to work much better for me than the actual site. For the uninitiated, Farecast serves up the current lowest prices for specific flights and a prediction (complete with a percent confidence rating) about whether the current price will rise or fall in the future. (It also gives a lengthy list of historical prices, the purpose of which, it seems, is to mock you for not making plans earlier.) At any rate, Farecast is a great innovation, and it's the next step up in utility from fare aggregating websites as Sidestep.com.
But Farecast is terrifying to use. First off, according to the Seattle Times, its predictions are only 61% accurate. And when it does tell you to wait for fares to drop, the resulting stress can be incredible, especially if you're in a major time crunch. For example, I was planning to fly out to Raleigh-Durham from San Francisco right before the Christmas holidays. Since I procrastinated until the week before, the prices for a round-trip ticket were almost a grand, and I was desperately hoping to pay much less. So I was thrilled when Farecast told me to hold off. The next day, prices had jumped up another $200, and the day after that, they were up again, though Farecast kept telling me to wait. I chickened out and ponied up the dough well before the price ever got close to the original one I saw, much less below it. As it turns out, the prices dropped steadily in the two days before my flight, and I could have picked up a ticket at the last second for almost $300 less than I paid. So thanks to Farecast, I felt like both a chump for paying and a weenie for not waiting.
Luckily, Farecast has devised a way for me to hedge my bets, called Fare Guard. For about $10, I can protect the original fare if Farecast predicts it will stay the same or drop. That means that they'll pay the difference if I end up buying a more expensive ticket later in the week. While a few people (including AOL's Rocky Agrawal) have noted that Fare Guard has many of the features of (generally useless) extended warranties, I've found that it definitely a needed stress-reliever when I'm buying high-priced tickets.