Man, there's no way this can be a non-volatile question, but the fact is that data can very easily determine an objective answer. To save the easily bored people out there some time, here's the answer: Yes, atheists are by and large smarter than religious people. But obviously I can't just write that without proffering some evidence.

Studies Showing That Atheists Are Smarter Than Religious People

I want to start this section out with possibly my favorite graphical representation of data on this topic. Here's a compiled set of data from each U.S. state comparing the religiousness of the state's population to factors such as IQ, poverty, crime rates, generosity, and political ideology. (Green is "favorable," while red is "unfavorable," with "religiousness" and "conservatism" obviously being subjectively colored in this case.):

Now, I'll likely refer to this image in future blogs for some of the different points that it makes, but for this particular blog entry the important columns are he first two. As you can see, there is a statistically significant negative correlation between IQ and religious belief.
A 2004 study by Regan Clark at UC Davis (PDF) also found a negative correlation between IQ and religiosity and spirituality.
Others also have graphed the average IQ of a country versus the percentage of the population that considers religion important, and they've produced graphs like this one:

(The U.S. is the outlying data point at 59,98)
There are also numerous polls of people considered "intellectually elite" that show most people in intellectual fields consider themselves atheists -- by a long shot.

A recent study on the matter concluded that intelligent people are more likely to "adopt evolutionarily novel preferences and values" such as atheism, monogomy (which is not within human nature and is not evolutionarily desirable), and liberalism.

Are Atheists Elitist?

Posting a blog entry like this simply bolsters the stereotype that atheists are elitist. So ... are they? The truth is that I can't think of a scenario wherein a staunch, vocal atheist isn't elitist. If an atheist is debating or explaining a scientific or logical concept to a religious person, how can that atheist not feel like the more rational, logical person in the debate? The atheist is attempting to use pillars of intellectual progress to point out the flaws in another person's belief system -- I don't think there's any way the person on that side of the debate can be committed to his position and not feel smarter than his opponent. So yes, vocal, passionate atheists certainly are elitist when dealing with religious people -- I just can't see any way around that claim.
However, does that mean that all atheists are elitist? It most certainly does not. Most of my non-believing friends are entirely content with a live-and-let-live philosophy of life. Many moderate atheists see religions as likely incorrect but not so far off-base that their adherents are mentally lacking. It is predominantly the most outspoken of atheists who feel intellectually superior to their religious counterparts.
And let's not forget the flip side of the coin. Devoutly religious people revel in a different kind of elitism; rather than feeling intellectually superior to atheists, most of them feel ... well ... holier than thou. Devoutly religious people feel morally superior to atheists (despite evidence indicating the opposite), and they also feel smug as a result of knowing a "truth" that atheists don't know -- like a special secret.
So, to be frank, the most passionate people on both sides of the debate come off as elitist assholes, but there's a key difference -- atheists have evidence to back up their elitist claims.

Correlation Vs. Causation

But hold on, does everything I've said above mean that you have to be an idiot to be religious? With that question posed, it is in good faith that I point out the difference between correlation and causation. When interpreting data and finding patterns, it is important to remember that just because two sets of data correlate, it does not automatically follow that one caused the other.
An excellent example of this fallacy comes from the Wikipedia page on correlation vs. causation. It is true that when ice cream sales increase, the rate of drowning deaths also increases quite dramatically. Without the distinction between correlation and causation, it is obvious that ice cream is the silent, drowning killer (and people obviously should stop eating gigantic ice cream cones in the bathtub). Those who understand the difference between correlation and causation understand that, of course, the two increases both are related to the fact that it's summer and people are simply eating more ice cream and swimming more during those months. So, summer is the silent, drowning killer. ;)
Back to the main point: Evidence shows that religious people are more likely to be less intelligent. It does not necessarily follow that most people are religious primarily because they're unintelligent or uneducated; both traits could be caused by a separate factor.

So Then What's the Cause?

First off, to clarify, I'm not saying that a lack of education and/or a lack of intelligence are conclusively off the hook as to the cause for religious belief, I'm simply saying that there may be an alternate cause for religious belief that also causes a lack of education.
In this case, the most likely alternate explanation is poverty. Poverty seems to be a unifying factor. If you rate all of the countries by both per-capita wealth and religiosity, the two lists sync up very well. The one outlier is the United States, which is disproportionately religious compared to the average wealth of its citizens (see graph at right). Yet even within the United States the trend continues; the more impoverished you are the more likely you are to be religious. Poverty alsoseems to be directly correlated with education; the more money you have the more likely you are to be educated and/or intelligent.
A prime example of poverty in action is the prison population. Prisons are predominantly full of uneducated, strongly religious minorities. From that set of data one could assume a few of things: 1) minorities are more likely to be bad people, 2) minorities are more likely to be dumb, 3) minorities are more likely to be religious. But wait, add to the evidence the fact that prisons inmates are more likely to be poor and you have another explanation: poor people are more likely to be uneducated, religious, and inclined to participate in criminal ventures. It just so happens that minorities simply are overrepresented among the poor.
I haven't seen a specific study on this (although I'm sure one's out there), but I hypothesize that if you correct for race you'll find that race is irrelevant and that poverty alone makes one more likely to be a religious, unintelligent criminal, regardless of race.

So, Religion IS Off The Hook Then

Nope, but nice try. The simple fact is that the more you know about science, logic, psychology, and rational thought -- in other words, the more intelligent you are -- the more likely you are to be an atheist. Here are the conclusions you can come to from the evidence:

• Being religious inclines people to be both unintelligent and poor (obviously unlikely)
• Being unintelligent inclines people to be both religious and poor (this certainly is possible)
• Being poor inclines people to be both religious and uneducated (also very possible)
• Being poor and being unintelligent/uneducated both contribute to a religious inclination (probably the most-likely scenario)
• All three are correlated, but caused by another factor (could be, but not as likely, although I'll grant that there could be more causes for religiosity in addition to lack of intelligence and lack of wealth)

Without a doubt the most likely conclusion is that a lack of intelligence is one of several factors that incline someone to be religious. Certainly wealthy people are religious, and certainly smart people are religious, but evidence shows that people who are neither wealthy nor smart are much more likely to be religious.

Anyway, go off and be elitist you atheistic jerks -- you've earned it.
-- The Atheist Apologist --