On the last page of the article, there was mention of "lowering the CPU temperature with liquid nitrogen or a Peltier to around 5C could yield even larger gains" but this is in need of some rephrasing.

We've worked with liquid nitrogen a fair amount, and temps are closer to -200C (see http://www.liquidnitrogenoverclocking.com/news_03.shtml for example).

As for Peltier Cooling, our experience has shown that you can't get more than a 40C difference compared to the ambient temperature. So, it would be much easier for a Peltier device to hit 5C in the winter somewhere cool than in the heat of summer.

Peltier devices are also very inefficient. It costs you about 10 times as much power to remove the "heat equivalent." By that I mean to pull away 50 Watts worth of heat would cost you 500 Watts worth of input power. Clearly, this is not the way to go.