When people ask me (as some Jehova’s Witnesses did only a few weeks ago) whether I’m an atheist or an agnostic, I say both. This often surprises people, whether they believe in God or not. I also find that many people interpret atheism to mean a certainty that there is no God, and agnosticism to mean that you can’t make your mind up.
I think this is misleading. Agnosticism is about knowledge and (a)theism is about belief. Maybe some people can’t make their mind up, but I’ve made up my mind that there’s very unlikely to be a God of the sort that religious people promote (although I admit to the occasional sneaking suspicion that capricious deities of the Greek or Norse kind might be a reasonable explanation for the world). This is why I say I’m an atheist. However, I accept that there are things beyond my ken, that all sorts of metaphysical situations are at least possible (maybe we’re all part of a computer game written by some celestial nerd kid in his Mum’s basement). Even Richard Dawkins doesn’t claim absolute certainty. In my experience, it’s the religious who claim that. This is why I call myself an agnostic: to distinguish myself from those who claim absolute knowledge on such matters.
I think most atheists are, strictly speaking, agnostics in the same sense. Religious people don’t always realise this, which is one of the reasons they often think atheism is inherently arrogant. Which is one of the reasons I don’t just drop the “agnostic” as uninformative.
My mother, for the record, describes herself as an agnostic Christian.