The Core

If it starts happening on a decent % of sites, it makes much more sense to have a toolbar installed that runs 1% of the time rather than inefficiently 100% of the time, especially so for GPU crypto. My mid-lower range laptop GPU can compute around 70M SHA1 hashes/sec, the JS implementations mine hundreds a second, even the webGL ones are quite slow.

Related idea: stick GPUs into cycling and rowing machines at gyms. Apparently a cyclist can generate up to 200W/h, more than enough for a GPU to do work. If they were to do something like protein folding, you're curing diseases while you get fit... should be easy to market that.

Same with wearable tech.

What ever happened to all those distributed computing efforts? SETI was first, but there were many other science projects that jumped on that wagon. I don't hear much about that anymore though

should be easy to market that.

Maybe...

RE SportsArts "green" equipment that puts energy back into the grid...

The reasons they are able to do this: 1. They are large enough ($100 million+ annual sales) to be able to do large production runs of the equipment, and 2. They are simply taking out old electronics and putting in new electronics. 

 - http://www.thegreenmicrogym.com/electricity-generating-equipment-2/

Also

 - http://content.time.com/time/business/article/0,8599,2032281,00.html
 - http://www.dailymail.co.uk/news/article-2430771/Worlds-self-powering-gym-uses-energy-WORKOUT-lights-dont-break.html