Apparently my search-fu is weak. Would you care to link, or suggest search terms that would make finding it less arduous?
EDIT: found it, I think, over here. One of the obvious issues is that it's not a credible threat.
So far I haven't seen a counter argument over there that satisfies me. If there is anywhere that they go into it more in depth, please do give it a link here.
Why not put all the search terms you tried during your search-fu session into a comment. That will make this less likely to happen in the future.
Now I tend not to follow this form very much, so please excuse me if this has been suggested before. Still, I don't know that there's anyone else on this board who could actually carry out these threats.
If anyone accepts a pascals mugging style trade off with full knowledge of the problem, then I will slowly torture to death 3^^^^3 sentient minds. Or a suitably higher number if they include a higher (plausible, from my external viewpoint) number. Rest assured I can at least match their raw computing power from where I am. Good luck.
EDIT: I'm told that Eleizer proposed a similar solution over here, although more eloquently then I have.