The discussion of the same paper on Overcoming Bias has reminded me of another striking correlation I read about recently:
http://www.marginalrevolution.com/marginalrevolution/2010/07/beer-makes-bud-wiser.html

It seems that for whatever reason, abstinence does correlate with lower performance on at least some tests of mental ability. The question is whether the controls in the study cover all the variables through which these lower abilities might have manifested themselves in practice; to me it seems quite plausible that the answer could be no.