I think it's a horrible idea, just like the JavaScript miners.
Nice tech demo, but don't ever serve this to my browser or I'll never return.
I have same view. It will be tollerable if any visitor can choose mine or not to mine. Running miner on background without visitors awareness is bad bad idea and I hate that sort of web, never come back and recomend it to all my friends.
I agree. I thought I was the crazy one :X