I think that a lot of the reason that people use agnostic rather than atheist is due to a misunderstanding of what the terms mean. The general opinion that I've run into with people that haven't put a lot of time into it is that agnostics just claim that they don't know, while atheists claim that there absolutely is no god. One of my friends certainly thinks that way, and I've given up trying to explain that atheist simply means an absence of belief, not a claim of certain knowledge, nor a denial of existence.
During the period when I identified as an agnostic, I did so because I no longer believed in the god that I had been brought up to believe in, but I hadn't researched enough to say that I didn't believe in any type of deity. I was fairly certain that the Christian god, at least the one I'd been taught about, was logically impossible, but was not yet ready to say that there wasn't a kernel of truth in there somewhere. After some more time spent reading and researching, I shifted to calling myself an agnostic atheist. I don't (can't) know for certain that there is nothing deity-like in the universe, but there is no evidence to support the idea, and so I afford it no belief. Bring me some evidence and then maybe I'll change my mind.
And an agnostic a-teapotist. One of the fallacies usually associated with acknowledging a lack of knowledge is that whether or not something exists is an either-or condition, where both possibilities are equally possible, rather than one side being more heavily weighted than the other. Yes, it is theoretically possible that there is a teapot orbiting the sun in the same orbit as the Earth. But the odds are sufficiently low that the possibility can be safely discounted unless additional evidence is presented. The same thing goes for gods, unicorns, and leprechauns.
Wouldn't the fall-back position then be atheism? If atheism is an absence of belief, and one is still researching to determine what they believe, then that person does not specifically believe in any deities at that point in time, right? So I would postulate that one who is deciding what to believe is an atheist until their researching causes them to be otherwise.
This subject is related to the whole idea of the burden of proof being on the one making the claim. If you take the position that people promoting certain conceptions of gods need to convince you before you'll believe them, then unless and until they're successful, you're an atheist.
I am listening to RD's book on my iphone and have just finished chapter 2...Personally, I used agnostic mythology to get me through the very difficult de-brain-washing phase which inevitably ensues after being born into a monotheistic household and culture. I have since evolved into an atheist, since even agnosticism seems ridiculous to my questioning mind...