Technique

Commenters to the previous post and Raffi at Waddling Kitchen point out that while recipe compendiums may well be rendered obsolete by the internet, serious cooking techniques (like most serious things, I guess) are still learned from books. Here's Raffi:

They are studied, pored over and mimicked by professional cooks across the country. They are the avenues through which the cutting edge is transformed into the quotidian. In other words, if you're eating sous vide short ribs in your local upscale restaurant in Oklahoma City, say, it's either because the cook there did a stage at Per Se (or the equivalent) or because they read and studied Under Pressure. That kind of cookbook simply isn't in competition with epicurious.