Have you compared running your code in JS on an ad-hoc cluster like this vs running it in optimized C on a local machine ?
On the other hand, a quick Haskell implementation using Data.Digest.Pure.SHA is doing about 6,000 hashes per second (might have been 8000, I forget now) per core on an Intel(R) Core(TM)2 Duo CPU E6750 @ 2.66GHz
So you're looking at 1000 people to equal one core of a decent desktop. It's certainly an interesting approach, and has a lot of potential. I'm just not sure the marketing is there with the "help us win" motivation.
good luck!