> Widget ethics. Using third-party processing power has usually been opt-in: people needed to install SETI@home or the BOINC software to lend their CPUs. JavaScript allows us to use people’s CPUs without their explicit consent just when they visit a page with the widget, which makes this a grey area.

This could be a new way of generating revenue from a website: selling time on visitors' machines. I'm not saying it's a good or ethical idea, but it's certainly an interesting idea.