Roadrunner, officially the world's fastest supercomputer, is used in nuclear weapons research. It can sustain just over 1 petaflop of performance, but is still slower than the Folding@Home network of computers. This network includes PCs, Macs, Linux Systems, and more recently (and importantly) the PlayStation 3.
The Folding@Home network of computers, which is used for functions such as Folding@Home, boasts more than 4.3 petaflop of computing power - the equivalent of more than 4,300 trillion calculations per second. PlayStation 3 users managed to achieve 1 petaflop of protein folding just 7 months after the application was release, pushing the Folding@home program to be recognized by the Guinness World Records folks as the most powerful distributed computer network in the world.