Some of my closest friends are religious...particularly Muslim.
I used to date a Muslim guy who is now my ex, but we are still best friends. It's not awkward at all, we really are good friends. He is a very 'devout' Muslim though. Actually, that's what he says, but I really don't think so since he has had sex before marriage, drinks alcohol socially, amongst other things.
But anyway, I don't think me apostatizing will affect him much, maybe he'll get a little annoyed and try to argue religion with me, but I really don't want to force my atheist views down his throat. He is a peaceful, kind and loving person and his faith isn't harming anybody, so I couldn't care less.
I have another friend, we haven't known each other long. He is on the blogosphere. He was fine with me being an apostate, one of the first few people whom I came out to (I haven't come out to my best friend yet as I want to do it in person and we are in different countries at the moment). More recently though, I think he has read my blog posts and isn't very happy. He hasn't responded, and normally steers well clear of my blog. I've seen his blog and he does tend to question things, but a lot of his visitors are Muslim so I guess he tip-toes around it.
Anyway, I talked to him recently on MSN and he seems a bit off with me....meh I will have to approach him soon.