I could imagine larger NGOs doing that, havng their supporters run the "mining bot" on their PCs to support a NGO or charity for instance
They'd be better off just writing a check to the charity. It will cost them a lot less.
I've already calculated that the break even for mining is 0.25 MHs/W.
Using your example of 1 MHs per CPU it needs to use less than 4 Watts to break even.
Any more than that and you are losing money.
A 5770 doing 200 MH/s needs to use less than 800 Watts to break even.
That's where the profit is.
Now if you could get some gaming club / forum to all chip in with their unused GPU cycles to donate to charity then it would make sense.