I'm a life-long non-believer who wishes Dawkin would shut up about religion.
For one thing, his smug, self-satisfied manner just gets my back up (and, no, that has nothing to do with his accent).
More importantly, his arguments are riddled with inconsistencies, unstated (and, for the most part, unfounded) assumptions, and rhetorical sleights-of-hand. Worse, he has consistently failed to address the very valid criticisms that have been made of his work on religion, instead retreating into "I'm no philosopher" populism whenever a point is raised that he can't handle.
To put it bluntly, there is a coherent case to be made against many aspects of religion, organised and otherwise, but Dawkins ain't making it. His work on subjects more closely tied to his actual field of expertise is usually coherent and often quite brilliant (though I still find his smugness irritating). But, whenever he has religion in his sights, the rigor which he brings to those other subjects seems to desert him.
I'd hazard a guess that the reason for this is that he has too great an emotional hang-up with religion in general, and with Christianity in particular, which leads him to become far less rational than usual when he engages with that subject. To use a rather trite analogy, he's like the ex-smoker (Dawkins was raised a Christian) who can't stop berating smokers about their habit, even though his exhortations tend to make those smokers less - rather than more - likely to give up.
If anyone wants a more specific explanation about the problems with Dawkins' arguments, I suggest they check out this article from the New York Review:
http://www.nybooks.com/articles/19775
It's not totally comprehensive, and there are a couple of points I take issue with, but it highlights several of Dawkins' most glaring problems.