Thanks for making the math, now if we consider that JS is slower by a factor of 1000 than regular GPU (http://news.ycombinator.com/item?id=2566442), and browsers are soon to implement WebGL, then it becomes $80/day.

And if it is a game and users stay on average for 10 minutes playing, that's $800 and you don't lose any resources on the server side, since it's a WebGL game.

It starts to getting interesting. I would be more interested in a game that consume my GPU in the dark than a one that wants me to click an ad and bother me with it.