[/size] Also - and apologies if this has been pointed out already and I have missed it - but all else aside, the study would be more valid if it were conducted within a single country, rather than comparing countries. Roughly the left-hand 50% of nations are third world, or at least, developing, where education and subsequently, measurable IQ, is incomparable to the nations on the right. Simultaneously, the majority of people there are subjected to a quality of life far harsher than those in the developed world, and far more ready to cry out for help to a supernatural source.
It also doesn't take into account nations like France, to the far right of the graph, which prides itself on being a fiercely secular nation, maintained by government policy.
Factors like these will affect the outcome, but not reflect thus. To gain a better comparison between IQ and religious belief, it would be preferable to gather results from a single nation, and preferably even subjects from similar geographic and socio-economic regions, thus avoiding data contamination.
All that said, props to Scaredgirl for encouraging a non-sectarian or overtly emotional debate!