Based on our FLOP estimate (see https://stats.foldingathome.org/os), Folding@home has passed the 5 petaflop mark recently. To put it in context, traditional supercomputers have just broken the 1 petaflop mark, and even that level of performance is very challenging to aggregate. The use of GPU's and Cell processors is has been key to this, and in fact the NVIDIA numbers alone have just passed 2 petaflops.
Thanks to all who have contributed and we look forward to the next major milestones to be crossed!