Without Google, Yahoo, and their brethren, using the Web would be like wandering through a library where a prankster has restacked the books at random. Still, sorting through thousands or millions of pages spurted out by a search engine can be nearly as overwhelming. Imagine instead being able to call on the group judgment of other users, people who are constantly skimming the latest Web content and arranging the best stuff into neatly labeled piles.

It's called tagging, and it's going on at a handful of free websites -- Del.icio.us, Flickr, Furl, and Rojo, among others -- where members are voluntarily classifying and categorizing thousands of pieces of content each day. The phenomenon is growing fast: Delicious alone had 90,000 total users by April 2005, up from 30,000 the previous December.