Sounds like a successful academic project but not so much for the industry. I'm hard pressed to find a company willing to use plain, publicly-available Javascript to write their number crunching algorithms. That said, I would loved to be proven wrong - good luck to you!
Berkley has a similar project going on where you can download a program that donates your idle CPU to their tasks.
Ok, but do the advertisers want you CPU processes or your screenspace?