Science fans find a lab on the Web

The Internet has opened up new opportunities for millions of so-called citizen scientists through participatory projects. As millions of people get involved, scientists are grappling with how best to harness the amateurs' enthusiasm.

Many got their first taste of citizen science with SETI@Home, which enlisted more than five million users in the search for extraterrestrial life. Volunteers downloaded a program that used their computers' idle processing cycles to sift through data from radio telescopes.

SETI@Home inspired other initiatives, like Grid Republic, a consortium of more than 50 projects, and IBM's World Community Grid, which is being used by Chinese researchers to investigate efficient water-filtering techniques.