What exactly is the line that no one wants to cross?

I write Christian fiction.  That's really all I can write...I've tried other stuff, usually unsuccessfully.  I just need to include what I believe in what I write.  That's why I enjoy reading Christian fiction--I know that I won't feel all yucky when I'm done.  

But, after years of reading various authors, I've found there's a big difference in how they approach faith in their works.  I admit, I've read a few books where I've been completely annoyed because it feels as though the writers are trying to convert me.  My personal thought on this (and, admittedly, I could be wrong) is that most people reading Christian fiction are already Christians. I get a little tired of reading pages of sermons planted in the story or Christian-ese filling the dialogue.  A little faith goes a long way. 

On the other hand, I've read a few authors where I had no idea that they were writing from a Christian perspective because some of the writing has been a little racy or the doctrine spouted by characters has been a little shaky.  

So, where is that line?  How do I write what I believe without either boring or offending the reader?  This is something I still struggle to find a balance with...I want to show my characters praying without going overboard.  And what about salvation?  How much detail should one go into if you have a character who accepts Christ?  All I can do is keep practicing and editing and praying myself for wisdom in what I write.