In a project called systemic (no capitalization), hundreds of amateurs around the world are using their PCs to sift through the mountains of data collected by professional astronomers, looking for the tiny gravitational anomalies that could signal undiscovered planets around other stars. Participants download the systemic console software, usable on Mac, Windows, and Linux computers. (See http://oklo.org/)
The Internet has proven to be a way for amateurs to swell the ranks of professionals in this and other scientific endeavors. Global networks of volunteers look for signs of alien intelligence, examine the light around distant stars for additional planetary clues, and even examine an archive of NASA images to detect grains of stellar material brought back to Earth by the Stardust probe.