From the article "Orbitz Reaches New Heights" in New Architect magazine (formerly Web Techniques):

The high-level algorithms are almost entirely in Lisp, one of the oldest programming languages. You're excused for chuckling, or saying "Why Lisp?" Although the language can be inefficient if used without extreme caution, it has a reputation for compactness. One line of Lisp can replace 20 lines of C. ITA's programmers, who learned the language inside and out while at MIT, note that LISP is highly effective if you ditch the prefabricated data structures. "We're something of a poster child for LISP these days," says Wertheimer. "Lisp vendors love us."

The downside of using a sometimes-maligned language is that it's hard to find good Lisp programmers. Today, only half of ITA's coders are Lisp gurus. For its own Web site, ITA relies on server-side Java, partly because of the availability of capable Java programmers.

Actually, there is no excuse for chuckling.