He did an interview with CT that is worth a read.  If you don’t have time, here are the highlights.

HJ: Before you visited churches, what were some of your assumptions about them? Were they right or wrong?

HM: Before, I thought church was a boring
place everyone was forced to go to on a Sunday morning and that there
was absolutely no thinking involved. I was wrong on those points. The
churches I saw knew how to bring people in and keep them there, and
several times, I heard sermons that raised ideas I had hardly thought
about. Of course, there were also sermons that put me to sleep, but not
as often as I thought they would. The people in the church chose to be
there, and so did many of their children.

HJ: You say in your book that your
interactions with Christians, for the most part, have always been good,
but they’re—we’re—not asking the right questions. What are some of
those questions that Christians need to be asking when we’re talking to
someone with different beliefs?

HM: You should ask: Are atheists really bad?
Why do we think other religions are wrong? And not just “I’m right, so
they’re inherently wrong,” but what really do they believe? Why
do so many people believe these other things? Why do only certain
people believe in Christianity? How do we know what’s divine? How do we
know every single thing the Bible says is true?

And I know some of these questions have been
answered in apologetics books, but it would be great if more regular
people, not just academics and authors, asked themselves these
questions. I think that might make their faith stronger—or maybe it’d
weaken it—but more than anything, it would get them thinking, to really
distinguish what they believe.

and

HJ: Did you experience negative things while visiting these churches?

HM: I heard a lot of what I considered to be
hate speech. Some churches led missionary trips with the intent to
“convert Muslims,” as if that was the reason some countries were
under-developed or impoverished.

Then, there were prayer services where people were
asking God for things I figured they could just take care of
themselves. You have a problem in your relationship? I think you should
talk to the other person and work it out. You don’t like your job? Then
work on finding one that suits your passions. I think atheists are a
lot more confident than Christians in their own abilities to make
things happen.

And a lot of people, because of this eBay thing,
they were like, “You need to read such-and-such book,” and they’d send
them to me. One of the titles someone sent me was I Don’t Have Enough Faith to Be an Atheist.
And it said something like, “If you are an atheist, you might as well
be killing everyone you meet and robbing all these stores.” I’m
thinking, someone actually believes that.

You can find the rest of it here: http://www.christianitytoday.com/outreach/articles/atheistwenttochurch.html