Now that airlines have almost completely transformed from a business necessity and personal luxury to a commodity service (with all the cattle-car charm that implies), fliers have realized The Truth Is Out There (on air ticket prices). Price opacity is the airline's best friend, for pricing's set with proprietary algorithms which drop prices for a few hours, ramp up until just before a flight, and if seats are unsold, sometimes drops again (unless it's Tuesday, then it's a Royal Fizzbin).
Expedia, Travelocity, Orbitz, Priceline, et al. were the consumer's first sources for information, followed by second-gen sites like Kayak which searches across multiple vendors, Farecast, which predicts changes and lets you hedge your bet, and Farecompare for historical price data.
Now, YAPTA, a free downloadable applet for IE/Windows (Firefox coming soon), scans prices for flights, and e-mails you when prices drop. With that data, as today's Wall Street Journal THE MIDDLE SEAT column (subscription required) notes, you can get a refund, and beta testers averaged $85 on such credits.
Bottom line: When you book a flight, you've now got a better chance than ever to know when to buy. Does it matter? Join the discussion.