For what they're worth. I've been posting on the atheist forums, just because I don't subscribe to any organized religion, but I wouldn't really call myself an atheist either because I do have some beliefs and ideas and I do feel there's a 'higher power' or divinity, if you will, though I don't call it God.
I see the biggest difference, really, being the difference between religious dogma and spirituality.
Most of the atheists on those forums are not angrily insisting there is no god, they just exercise the right not to choose organized religion - most of them do seem to have beliefs of a spiritual nature. There were a few that really feel that Science and evolution explain it all away but I can't speak for the others, only me.
Anyway, this difference between religious dogma and spirituality is, to me, the biggest difference between atheists and christians and this other person in the thread who talks about "ego" is being a bit unfair in her/his suppostions. "Atheism" is a self-proclaimed term basicially meaning lack of "theism" or lack of organized religion. I think when most people hear that term, they see it almost as a cult of sorts - the "I won't believe it till I see it" sect.
I was surprised to find that most atheists, like myself, have a pretty solid belief system, we just don't have a huge building erected and get a bunch of people together and take their money in celebration of it.
Furthermore, I think many rebel (I know I do) against the fear-mongering and hate-breeding of many of the fundamentalist Christians - those are the ones that seem to be driven into evangelical fervor at the very thought of an atheist in need of conversion. It's unfair of them to assume that if someone believes differently that they are automatically wrong and doomed to a life of eternal bar-b-que.
That pretty much explains my few thoughts on the subject.