I am speaking for myself, as an atheist. I would not presume to speak for other atheists. I hope they will let me know where they agree and where they disagree, but we all know they are a silent group, so maybe they won't.
The problem I have is one of perspective. I know this will seem trivial to many, but I don't think it is trivial. I feel that I have an ABSENCE of belief in god, not that I DISBELIEVE in god. The reason is thus:
AN ABSENCE of belief indicates thats there is nothing there. In many cases, I may never even have given that "god" a first thought, much less a second thought. Sorry that this offends people, but I see gods/religion as just a more elaborate (in some instances) fairy tale developed to help people feel better about themselves and the world around them. I reject fairy tales. I do not believe in any of them. As a matter of fact, I can't remember a time when I did believe fairy tales (though I can remember being a Catholic) though I am sure there was a time. See that is an ABSENCE of believe.
A DISBELIEF is something different. Perhaps an analogy (and, believe me, I am hoping Evoman comes up with another scene to his play on this thread) would help. I love the Minnesota Vikings (it has been a rocky 35 years of my life being a fan, but I am still loyal). Let's say I "believe" they are the best team ever (no snide Vikings comments, I'm trying to make a point). Let's say there are a whole group of us that believe they are they best team ever (a small group to be sure). You, on the other hand, don't give a rip about football. You don't watch it, don't keep up with it, couldn't even name more than a handful of the more visible teams, have no idea who won the Super Bowl last year, heck, you don't even know what the Super Bowl is. If you were talking to me and my friends, and I said "Hey, this guy/gal doesn't believe that the Vikings are the best team ever," that would be a mis-statement. You have absolutely no thoughts about the Vikings in comparison to other teams or as a team in and of themselves. The way I worded it, assumes that the Vikings are the best team ever, but you just choose to not acknowledge it.
Do you see the connection to religion? To say to me that I disbelieve that Jesus is God (or whatever sect) is to assume that he is. I just am too stupid to realize it or willfully ignore the divinity. And that isn't the case. He is a fiction just like every other mythology developed by humans to create some false security.
On edit: I think this is closely related to BMUS' thoughts on believing. I could never believe in god again, even if I wanted to.