I don't mind if the candidates are religious. Atheists are a tiny minority in this country and most people have wouldn't vote for one, and I might not like it, but I accept it. So a candidate being personally religious and making the occasional religious remark is something I will grudgingly accept.
However, what I absolutely WILL NOT accept is if the candidate is so religious that he feels compelled to inflict his religion on me. And Bush, despite making one offhand comment (that, unlike Brown, I DO think was intended as a thinly disguised insult) to the contrary has shown by his actions that he is quite happy to force his religion on others (witness his support of the anti Gay marriage amendment. I have never heard a decent non-religious reason to oppose Gay Marriage), or at the very least to openly and shamelessly pander to religious groups that want to impose their religion on everyone else.
I don't know if Kerry will be as bad, but it would be hard for him to be worse. Frankly, he doesn't strike me as the type, though. So though Kerry might be somewhat religious, I have to give it to Kerry on the religiousity issue.