Well, not quite sure on how combining Christianity with atheism would work. Combining some of the christian values (personal/social) with atheism is doable and quite common, but the rest.. not quite.
Totally agree on the second part. I only think about atheism at all when I'm confronted with religion or a more or less direct question about religion (either about the religion itself, or something social that gets evaluated based on a religion). To some extent I do think that even the more vocal atheists are basically acting on reaction, just being more socially involved (of course there are also always people set on enlightening you about stuff, wether religious or not). Otherwise as far as religious beliefs go, atheism is simply a state of not being of any religion/theist belief, it doesn't have any guidelines of behaviour.
