Besides the obvious safety and monetary concerns, whats to stop someone from using mercury in place of water to cool a CPU or GPU? Water (k=.58) is 3x better than alcohol (k=.17) and mercury (k=8) is 14x better than water at removing heat. (k = W/mK). It would obviosuly be heavy and require a more powerful pump than a water loop. Also, spilling it would cause major chaos. But besides the caveats, why haven't I seen someone do this? I mean, I've even seen ln2. using mercury isn't much of a stretch.