The World Wide Web has become a dense forest of information and images. Finding and keeping track of the useful, the valuable, and the interesting in that wilderness, even with the help of increasingly sophisticated search engines and feature-rich web browsers, isn't easy. But you're not alone out there, and the ever-innovative denizens of Web 2.0 have evolved a technique that allows you and your fellow travelers to mark your trails and drop a few bread crumbs along the way. It's called social bookmarking, and here's how it works.