John Allen Paulos is generally an entertaining and intelligent writer, but Irreligion: A Mathematician Explains why the Arguments for G-d Just Don't Add Up may be the exception. A few thoughts:
1) If you try to use a saw to drive in a nail or a hammer to cut wood, you will probably not be successful, though I doubt anyone would conclude that nails and wood are therefore faulty building materials. Even if you use a saw to cut wood, I can attest from personal experience that your chances of accuracy and success are not the same as a carpenter's. Please, Mr. Paulos, stick to using math and logic to explain math and logic. These are not necessarily the best tools to analyze religion, and when wielded by an amateur the risk of harm outweighs any chance of good.
2) Imagine a two page summary of a book hundreds of pages long written by the most respected brain surgeons in the world. Imagine the summary concluding that these experts are wrong. Imagine the summary written by someone whose regular job is a plumber. Now you have a taste of Irreligion. I kid you not that most chapters are less than five pages, nor do I kid you that in less reading time than it takes for the commercials to play in a TV break Paulos thinks he has summarized and demolished centuries of philosophical speculation. The single word ga'avah kept running through my head.
3) Is there anyone out there who woke up one morning and said, "Eureka, I now believe because the ontological proof is so convincing!", or who went to sleep muttering, "I'm glad I read that proof by design because now I can resume praying"? I'm pretty confident that is not how faith works. If the "proofs" that Paulos addresses are not the cause of belief, can shattering them really call into question the reasons for anyone's faith?