PZ Myers at Pharyngula has come under some criticism after having denounced what he refers to as "Dictionary Atheists"—atheists who define atheism negatively, as simple lack of belief in god, rather than affirmatively, as belief that there is no god.
I'm with Myers part of the way: I think atheism should be used to refer to people who believe that there is no god, plus noncognitivists; as with Myers, one of my main reasons for this is that people who call themselves atheists nearly always have affirmative reasons for believing that there is no god. We can argue about history or etymology, but the purely negative definition is too loose to map properly (as far as I can tell) onto the people who actually apply the label to themselves. If I were still agnostic, I would not want constantly to have to say, "Yes, I am an atheist in the technical sense of the term, but I am different from most people who apply the term to themselves, so I don't want to use that word." Nor, as an atheist, do I want constantly to have to say, "Yes, I am an atheist, and, furthermore, I actually believe that there is no god." Best to reserve the term atheism for the narrower category of affirmative disbelief, and the term nonbelief for the broader category of lack of belief.
Where I part with Myers is that he seems—and there is a good chance that I am misunderstanding him, here—to be trying to push atheism into the status of a more comprehensive worldview, complete with a particular epistemology and a particular ethic. I think it is best to take atheism only as a component of many different types of worldviews—an affirmative component, to be sure, but not a worldview itself. Again, my argument simply is based on usage. When people say, "I'm an atheist," I don't think they are saying "I'm an empiricist," or "I'm a skeptic about the paranormal," or "I have liberal social and political views," even if most people who call themselves atheists actually fit into all four categories.
Where I come back again to Myers—and this, I think, was his real point—is that precious little depends upon this debate, and most of the time spent on it is time wasted. All that matters is that you are clear by what you mean by your terms, when you talk to others, so they can understand what you are claiming and what you are not. But that is just the groundwork—everything of interest comes after that, when you have to defend the position you have marked out for yourself.
See What is atheism? for a rehash. Well, actually, this post is a rehash. So, I guess the linked article is a prehash.