I've participated in a lot of these distributed computing efforts, starting with SETI, then F@H, and I tried "United Devices" which is some other protein folding project.
In fact, I made sure all my computers had one of those running on it, since I didn't want those cycles to go to waste. That was, until, I got my laptop.
Laptops, as I'm sure you know, are great at power moderation. They'll speed up and cool the CPU in direct response to processes and instructions being run through them. When I first got my laptop, I loaded up F@H right after I installed windows. But when I tried to go to class, I found my fan would run full speed, my lap would heat up, and I'd get 2 hours of battery max.
Ok fine, turn off F@H when battery is being used. But when I was plugged into the wall, my computer sounded like a jet plane. Maybe that's because it's a cheap Dell, but the point is, my CPU was being used to it's MAX at all times, to the point where the area around me would be noticeably warmer (at least in the summer).
What this is all boiling down to for me is the immediate environmental impact. When I'm not using all the resources on my computer, cycles are NOT going to waste, because I'm saving energy. Another issue (a minor one, but noteable) is possibly shortening the life of your CPU, CPU fan, or other hardware. They may not seem like big issues, but that's the point of distributed computing: together we have an impact.
I also find that when I'm running F@H, I WANT to leave my computer running, if not for humanity then for the SAGoon team score. But that's not the right mentality. I'm not sure how desktop computers work, i.e. if modern ones have advanced power usage. I understand using spare cycles if you have servers or other machines running that would otherwise be using the same amount of power without F@H running. But processes require signal, and signals require current flow. It adds up.
Distributed computing for researching protein folding may or may not be successful. Right now I see it more as an experiment into whether researchers can used distributed networks to do their research. What we do know is that electricity usage and power production ARE immediate concerns, and the mentality that we should turn off our machines when we're not using them is something that can have an immediate and proven effect TODAY. Smog levels from the combustion of fossil fuels are just as much a concern as genetic disorders. Both cause sickness, and the former can cause the latter.
I hope you can understand my reasoning, and if you do, perhaps you could post the gist of this point in the "reasons not to fold" list.
Once again, I apologize for the long message, but thank you for taking the time to hear me,
-Wab