[brookst]

I mean coal power plants work, so building new ones is not stupid by that standard.

I think we have to expand the definition of stupid to include things that work but have net negative externalities. Not sure where PoW falls in that way of looking at things, but we should at least consider it.

(Thinking about it, Captcha is PoW, just theoretically work by the human)

[tarpitt]

Necroing this, but perhaps you might be interested in some sort of BOINC-like PoW scheme for websites. This was a distributed computing project originially known as Seti@Home. It's not really practical for cryptocurrency PoW applications (despite its use in Gridcoin) due to the centralized nature of the challenge-response, but certainly more useful than captchas or hashes!